How much time do you think it would take to check all of the possible powers and ECU connections that could cause the problems as described ?
Is there a strategy in play or would you be checking things for the sake of just doing something? If the time that you were going to be paid for doing that expired, how much more testing would you do (on your own dime, for free)?
How much time do you think it would take to check all of the possible powers and ECU connections that could cause the problems as described ?
Is there a strategy in play or would you be checking things for the sake of just doing something? If the time that you were going to be paid for doing that expired, how much more testing would you do (on your own dime, for free)?
All my testing is on my own dime for free, of course. How much time would it take me to check for loose connections in the major areas? hmmm... maybe 15 minutes.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
How much time do you think it would take to check all of the possible powers and ECU connections that could cause the problems as described ?
All my testing is on my own dime for free, of course. How much time would it take me to check for loose connections in the major areas? hmmm... maybe 15 minutes.
Problems like this Focus when presented show just how complex doing diagnostics of the computer controls can be on today's cars. But yet with a real game plan manageable without doing a lot of random testing. Before you test for a power supply problem or a poor ground connection you have to gain reasonable proof that the failure is likely based on all of the information that you can gather.
Take the codes. Use Google if you want and look up the definitions for each of them. Then make a logic table of what modules set which codes and see if there is a pattern to them.
That would take me far longer than jiggling some connections to see what comes loose, so I'm completing my step first. I know you and I differ on this approach, and I'm Ok with that.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Ford strategy way back in the 80's had technicians perform wiggle tests. Follow that routine enough times and you will wiggle a wiring harness, have a circuit failure resolve itself and leave you not having any idea of exactly what changed. You won't know if your wiggling the harness caused the change or if it was just a coincidence. If wiggling the harness actually did cause the circuit condition to change, and you didn't measure first and know for certain which circuit was failed and how it was failed you still wouldn't have enough reliable information to efficiently analyze the failure. It's not just about our differing on this, its about learning why it doesn't work most of the time and occasionally when it does how it often leads to the technician failing to solve the problem the first time.
Ford strategy way back in the 80's had technicians perform wiggle tests. Follow that routine enough times and you will wiggle a wiring harness, have a circuit failure resolve itself and leave you not having any idea of exactly what changed. You won't know if your wiggling the harness caused the change or if it was just a coincidence. If wiggling the harness actually did cause the circuit condition to change, and you didn't measure first and know for certain which circuit was failed and how it was failed you still wouldn't have enough reliable information to efficiently analyze the failure. It's not just about our differing on this, its about learning why it doesn't work most of the time and occasionally when it does how it often leads to the technician failing to solve the problem the first time.
But, don't forget: the reason our methods differ is because I am working on my own vehicles, not answering to a customer. If checking for loose connections solves my problem, nothing else much matters to me.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
But, don't forget: the reason our methods differ is because I am working on my own vehicles, not answering to a customer. If checking for loose connections solves my problem, nothing else much matters to me.
I haven't forgotten that, and its part of the point. Flawed methods that give the appearance of being a simple answer to a complex question are praised by just about everyone. The reason for that is because they don't recognize the failures that they cause and they base their whole perception on the occasional success. Meanwhile for the professional technician it raises a conflict that works to discourage always taking a disciplined approach to the work each and every time.
Consider this. It would take you more than a half an hour just to check the battery cable connections because you have to remove the wiper linkage for access. There is even more difficulty involved in trying to check connections at the under hood power distribution center and the smart junction block under the dash. The difficulty with just doing those checks would easily persuade someone to choose a different starting point since they don't have real proof of an issue with a portion of a given circuit to guide them. When difficulty of access discourages someone from taking their regular approach it gets more likely they are going to fail. Now if they had measured system voltage first and put a load on that power supply and saw the available voltage drop, then the game changes completely and now they have a real reason to check the connections that would be in play.
Here is what service information says about one of the codes the Focus had set.
Here is the trouble tree for U0100
When pressured to take the easy way out, you will have people changing modules just like that trouble tree says to do. There has to be a better way than just following a trouble tree, and there is.
Consider this. It would take you more than a half an hour just to check the battery cable connections because you have to remove the wiper linkage for access. There is even more difficulty involved in trying to check connections at the under hood power distribution center and the smart junction block under the dash. The difficulty with just doing those checks would easily persuade someone to choose a different starting point since they don't have real proof of an issue with a portion of a given circuit to guide them. When difficulty of access discourages someone from taking their regular approach it gets more likely they are going to fail. Now if they had measured system voltage first and put a load on that power supply and saw the available voltage drop, then the game changes completely and now they have a real reason to check the connections that would be in play.
Oh, see, there's the problem. No way would I purchase a car that requires me to remove wiper linkage to access battery connections. ;b
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Oh, see, there's the problem. No way would I purchase a car that requires me to remove wiper linkage to access battery connections. ;b
And at my nearest Ford dealer the linkage would probably be reinstalled backwards and the wipers would end up wiping the hood.
Did I mention a Pep Boys installing one of my tires with the letters "Outside" on the inside of the wheel. 3 out of 4 is a C in school, but at a business it's an F.
'18 Porsche Macan Turbo, '16 Audi TTS, Wife's '19 VW Tiguan SEL 4-Motion
Well it may not succeed because there are multiple causes for this problem, and he's just guessing. However, as far as guesses go, it's not an unreasonable guess by any means.
Did I mention a Pep Boys installing one of my tires with the letters "Outside" on the inside of the wheel. 3 out of 4 is a C in school, but at a business it's an F.
Really? You were there having the work done and even if it was flawed they still won the day. That's an infinite increase in revenue over what a more qualified shop and tech would have made for that service.
Did I mention a Pep Boys installing one of my tires with the letters "Outside" on the inside of the wheel. 3 out of 4 is a C in school, but at a business it's an F.
Really? You were there having the work done and even if it was flawed they still won the day. That's an infinite increase in revenue over what a more qualified shop and tech would have made for that service.
Well, not exactly. They had to dismount and remount the tire on the wheel correctly (re-work) and then they asked me what a suitable outcome for the wasted time was; I told them refund 25% of what you charged me since only 75% of the work was done right, and so I got like $20 bucks back. They claimed the chip on the rim wasn't caused by them and wasn't consistent with "shop" damage. I tend to agree, it was like a high speed rock chip or something.
'18 Porsche Macan Turbo, '16 Audi TTS, Wife's '19 VW Tiguan SEL 4-Motion
A couple weeks ago I posted a bunch of trouble codes that were being set in a number of modules of a 2014 Ford Focus. What a tech has to do with those codes first is build a logic table to see if there are any paterns revealed that would point more than one finger at any given module. The failure with this particular vehicle didn't expose any one module as the culprit which meant that either the failure was directly with the wiring that makes up the data bus or else it was a given module hogging up the bus and talking ontop of the other modules. What that means for the technician is the diagnostics are going to rely heavily on the oscilloscope and depending on what is seen in the voltage waveforms and under exactly what conditions the failure occurs it may be necessary to start knocking modules off of the data bus either by separating the bus, or by unplugging certian modules.
There is no way around the potential that this might be very labor intensive and once dissasembled if it is proven that one of the modules is to blame the vehicle will be down until the repair is completed. That also meant that the shop would have to have a current subscription for the factory scan tool especially if the module would need to be programmed after it is installed.
Here is a capture from the digital oscilloscope when the problem was occurring.
Here I zoomed in further.
As high tech as this is, part of the diagnostics also relied heavily on that learned feel that is almost a sixth sense that a tech has to gain through experience. A tech often has to be feeling exactly how the vehicle is being operated when the failure starts to occur and if the failure can somehow be forced to repeat. I'm not going to give that away for the moment. Instead I'm going to ask you to imagine and then try to explain what that might entail.
It's got a hiccup, like my old mower did when I replaced the wire going to the ignition coil and it was too long. Frayed a bit and then with every revolution of the flywheel, it would short out.
It's got a very specific failure and the capture proves beyond all doubt what it is, but not where it is. That part still took some creativity to avoid a lot of the physical labor that otherwise would have been required.
We have had pieces of this discussion in the past but its worth repeating right now. A computer and software written by some engineer WOULD NOT be able to figure out what was wrong with this car. Even the trouble tree's that engineers write cannot lead a technician to locate the failure because the circuit works the majority of the time and only momentarily fails under very specific conditions. (REM . Trouble trees only work with hard failures and are useless for random issues.) The closest the system can come with self diagnostics are the codes that the modules can report that show data bus voltage errors and modules that failed to communicate to each other. As said before the modules cannot test beyond their connector and never will. They can measure the voltage of the signal that gets to them, but have no way to know why it isn't within the programmed range when a problem occurs. That means it comes down to the technician having the training, tools and experience to deal with this stuff. A recent post in the iATN discussed a similar type failure on a 2017 GM and that car had some fifteen different data networks meaning the complexity and number of possible failures increased exponentially over this Focus.
Now take the rest of the environment that technicians have worked under for decades and realize that the easier work is over rewarded and work at this level has never paid the techs fairly for mastering the required skills. Soon you will find out just how few technicians there really are that can handle this stuff and because of what we have had to go through during our careers you actually don't deserve to have any at all.
What is the scope connected to? Is it connected to the system bus where all of the systems communicate simultaneously or is it connected to the instrument cluster?
What is the red signal vs. blue signal?
This is a voltage graph? The signals both shift down, the red signal inverts, and both get muddy in a random fashion. I'd say that red inversion is key to the problem but I am guessing.
When the customer first showed up with the Focus he provided a lot of information, some of which was valid and some very misleading. The problem had occurred when it was raining and he wanted to associate the problem to the weather. So he took the car and ran it through a car wash and a little later after he got the car to the shop, the symptom occurred. The initial captures and trouble codes were retrieved at that time but he couldn't leave the car because I was going out of town so plans were set to have it dropped off and in the meantime I could come up with a plan to approach this.
BTW. Remember the battery? It passed the electronic test, but failed a regular battery load test miserably. When I took the initial look at this I heard it crank slow during a restart which led to testing the battery. I had him get a battery while I was away so that we wouldn't have to be dealt with that when he was to drop the car back off. So much for a computerized tool telling someone what to do.......The battery was bad, but had nothing to do with "The Problem".
The conditions that actually made the symptom occur wasn't weather, it was simply how long the vehicle had run and if it was shut down and then restarted. Essentially heat was making something change. But, leaving the car just sit and idle did not cause the symptom to occur. In fact, shutting it off after it had run for about an hour and then restarting after it sat for a few minutes also didn't make the problem occur. However driving it after the heat soak did.
That was the critical first step in identifying the problem, figure out how to make it repeatable.
At first the distortion visible in the communication waveform was very random and at times appeared related to bumps and closed throttle decelerations. But was it really? Given that perspective I tried reversing and that definitely made it happen. The video linked was achieved by allowing the car to drift backwards down a light grade and stopping. It took a couple tries but the one time resulted in the failure repeating at an idle as is seen above. Based on that observation the failure was occurring with the engine moving the under-hood wiring harness.
The scope captures above show what the failure is, but not where.
Being able to influence the failure based on how the car was being driven and the fact that some bumps caused the signal to spike and not necessarily result in the system failing meant inspecting the wiring harness to the affected modules was necessary. Here is what I found in the harness that goes to the electronic power steering.
The CAN low communication wire is visible in the damage. It was abraded and randomly grounding so this is an easy fix at this point. But what does this information really mean to anyone else? Nothing. Anyone can parrot inspect a harness for damage, but with a circuit like this that runs to different modules that are scattered all over the car, you are looking for a needle in the haystack if all you know how to do is look. As a tech you don't get paid to look for something that you don't know is there or not.
Without the ability to measure the signals and see that it is getting randomly pulled to ground you have no way to know if there is even a problem with the harness. This could easily have been any one of the modules failing and hogging up the data bus. That being said it would also have been easy for someone to guess the instrument cluster based on the visual symptoms it was displaying. There is no shortage of people who would condemn a failed attempt to short-cut the diagnostics such as replacing just the battery and thinking this could be fixed, or the instrument cluster because you didn't know how to test and prove what was going on. The majority of mis-diagnosis is directly caused by not rewarding techs for following a disciplined routine and even worse disparaging them when they do. I can just hear someone trying to suggest that the harness should have been looked at first but that is really just a lack of experience and knowledge on their part. Nobody knew what the failure was until it was proven, and the odds are that it may never happen again.
Yep, just like my Briggs and Stratton wire. Abraded and randomly grounding
Took a real mechanic to figure that one out too.
But he didn't need a scope, he just popped the cover and eyeballed stuff. And if you had put the Ford on a lift you could have done a visual inspection with a good shop light and ruled the visible parts of the harness out in 10 minutes.
But he didn't need a scope, he just popped the cover and eyeballed stuff. And if you had put the Ford on a lift you could have done a visual inspection with a good shop light and ruled the visible parts of the harness out in 10 minutes.
With the description of the symptoms being that the instrument cluster was shutting down/ not working and the car failing to start when that happened, how do you logically make any association to the wiring harness for the steering rack? Ans. You don't.
This is the disconnect that often occurs and your entire routine is based on already having the answer in hand as was provided here. Prior to that you don't actually have any reason to put the car in the air and remove the ground effects so that the lower engine bay is even visible. (Oh, you didn't know that either did you?) What you did was move the finish line without having paid the dues to earn the insight that was necessary and that's exactly what has happened that has led to techs not being rewarded for doing the job the right way the first time. FWIW the wiring harness could have been damaged near any one of the other 12 modules that are, or could be on that data bus. That means the problem easily could have been inside any one of the doors. If that had been the answer provided you would then have said the same thing about just taking the door panel off and seeing the failure . But wait, we still have the problem that there wasn't proof that the harness was damaged until after I proved that was the case. Before that moment the car had all of the classic symptoms of a module such as the instrument cluster disrupting communication so maybe before you back guessed about putting the car in the air and looking at the harness you should have said to remove the instrument cluster from the circuit and inspect that harness first.
This all comes down to you (FWIW nobody did, not even me) had any idea where to look, nor why until after the critical details were gathered and then handed to you here by me. That information was collected using tools and routines and experience that you don't have and didn't even know were possible, let alone necessary. In the past our critics often played your game where they thought themselves fit to judge when they where themselves totally incompetent with the work that needed to be performed. The only difference here is we both know that you had zero chance of solving this no matter how much you pretend that someone could have somehow guessed right. BTW. That also goes back to the battery. Anyone who guessed that it could be bad would have gotten that correct, but it wasn't "the problem" and they would have easily been represented as having ripped the customer off by selling it.
And I think some decent software could have ID'd the wiring fault down to the exact wiring and even estimated the location to within a half inch. Really, if you have to run copper in a harsh environment, the wiring should be self-diagnosing itself all the time.
Cars are a pretty primitive collection of parts when you get right down to it.
Comments
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Mine: 1995 318ti Club Sport-2020 C43-1996 Speed Triple Challenge Cup Replica
Wife's: 2021 Sahara 4xe
Son's: 2018 330i xDrive
Is there a strategy in play or would you be checking things for the sake of just doing something? If the time that you were going to be paid for doing that expired, how much more testing would you do (on your own dime, for free)?
What's the big clue, that it's a manual transmission?
this tool State of charge is 50% and passes.
Next?
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Take the codes. Use Google if you want and look up the definitions for each of them.
Then make a logic table of what modules set which codes and see if there is a pattern to them.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Ford strategy way back in the 80's had technicians perform wiggle tests. Follow that routine enough times and you will wiggle a wiring harness, have a circuit failure resolve itself and leave you not having any idea of exactly what changed. You won't know if your wiggling the harness caused the change or if it was just a coincidence. If wiggling the harness actually did cause the circuit condition to change, and you didn't measure first and know for certain which circuit was failed and how it was failed you still wouldn't have enough reliable information to efficiently analyze the failure. It's not just about our differing on this, its about learning why it doesn't work most of the time and occasionally when it does how it often leads to the technician failing to solve the problem the first time.
Try and explain to him why what he wants to do is more likely to fail than succeed.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Consider this. It would take you more than a half an hour just to check the battery cable connections because you have to remove the wiper linkage for access. There is even more difficulty involved in trying to check connections at the under hood power distribution center and the smart junction block under the dash. The difficulty with just doing those checks would easily persuade someone to choose a different starting point since they don't have real proof of an issue with a portion of a given circuit to guide them. When difficulty of access discourages someone from taking their regular approach it gets more likely they are going to fail. Now if they had measured system voltage first and put a load on that power supply and saw the available voltage drop, then the game changes completely and now they have a real reason to check the connections that would be in play.
Here is what service information says about one of the codes the Focus had set.
Here is the trouble tree for U0100
When pressured to take the easy way out, you will have people changing modules just like that trouble tree says to do. There has to be a better way than just following a trouble tree, and there is.
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
Mine: 1995 318ti Club Sport-2020 C43-1996 Speed Triple Challenge Cup Replica
Wife's: 2021 Sahara 4xe
Son's: 2018 330i xDrive
It builds character.
Mine: 1995 318ti Club Sport-2020 C43-1996 Speed Triple Challenge Cup Replica
Wife's: 2021 Sahara 4xe
Son's: 2018 330i xDrive
'11 GMC Sierra 1500; '98 Alfa 156 2.0TS; '08 Maser QP; '67 Coronet R/T; '13 Fiat 500c; '20 S90 T6; '22 MB Sprinter 2500 4x4 diesel; '97 Suzuki R Wagon; '96 Opel Astra; '11 Mini Cooper S
There is no way around the potential that this might be very labor intensive and once dissasembled if it is proven that one of the modules is to blame the vehicle will be down until the repair is completed. That also meant that the shop would have to have a current subscription for the factory scan tool especially if the module would need to be programmed after it is installed.
Here is a capture from the digital oscilloscope when the problem was occurring.
Here I zoomed in further.
As high tech as this is, part of the diagnostics also relied heavily on that learned feel that is almost a sixth sense that a tech has to gain through experience. A tech often has to be feeling exactly how the vehicle is being operated when the failure starts to occur and if the failure can somehow be forced to repeat. I'm not going to give that away for the moment. Instead I'm going to ask you to imagine and then try to explain what that might entail.
Is this enough to suggest the need to concentrate the testing with the instrument cluster?
What is happening to the communication as viewed on the scope?
Now take the rest of the environment that technicians have worked under for decades and realize that the easier work is over rewarded and work at this level has never paid the techs fairly for mastering the required skills. Soon you will find out just how few technicians there really are that can handle this stuff and because of what we have had to go through during our careers you actually don't deserve to have any at all.
And never say never.
What is the red signal vs. blue signal?
This is a voltage graph? The signals both shift down, the red signal inverts, and both get muddy in a random fashion. I'd say that red inversion is key to the problem but I am guessing.
BTW. Remember the battery? It passed the electronic test, but failed a regular battery load test miserably. When I took the initial look at this I heard it crank slow during a restart which led to testing the battery. I had him get a battery while I was away so that we wouldn't have to be dealt with that when he was to drop the car back off. So much for a computerized tool telling someone what to do.......The battery was bad, but had nothing to do with "The Problem".
The conditions that actually made the symptom occur wasn't weather, it was simply how long the vehicle had run and if it was shut down and then restarted. Essentially heat was making something change. But, leaving the car just sit and idle did not cause the symptom to occur. In fact, shutting it off after it had run for about an hour and then restarting after it sat for a few minutes also didn't make the problem occur. However driving it after the heat soak did.
That was the critical first step in identifying the problem, figure out how to make it repeatable.
At first the distortion visible in the communication waveform was very random and at times appeared related to bumps and closed throttle decelerations. But was it really? Given that perspective I tried reversing and that definitely made it happen. The video linked was achieved by allowing the car to drift backwards down a light grade and stopping. It took a couple tries but the one time resulted in the failure repeating at an idle as is seen above. Based on that observation the failure was occurring with the engine moving the under-hood wiring harness.
The scope captures above show what the failure is, but not where.
Being able to influence the failure based on how the car was being driven and the fact that some bumps caused the signal to spike and not necessarily result in the system failing meant inspecting the wiring harness to the affected modules was necessary. Here is what I found in the harness that goes to the electronic power steering.
The CAN low communication wire is visible in the damage. It was abraded and randomly grounding so this is an easy fix at this point. But what does this information really mean to anyone else? Nothing. Anyone can parrot inspect a harness for damage, but with a circuit like this that runs to different modules that are scattered all over the car, you are looking for a needle in the haystack if all you know how to do is look. As a tech you don't get paid to look for something that you don't know is there or not.
Without the ability to measure the signals and see that it is getting randomly pulled to ground you have no way to know if there is even a problem with the harness. This could easily have been any one of the modules failing and hogging up the data bus. That being said it would also have been easy for someone to guess the instrument cluster based on the visual symptoms it was displaying. There is no shortage of people who would condemn a failed attempt to short-cut the diagnostics such as replacing just the battery and thinking this could be fixed, or the instrument cluster because you didn't know how to test and prove what was going on. The majority of mis-diagnosis is directly caused by not rewarding techs for following a disciplined routine and even worse disparaging them when they do. I can just hear someone trying to suggest that the harness should have been looked at first but that is really just a lack of experience and knowledge on their part. Nobody knew what the failure was until it was proven, and the odds are that it may never happen again.
Took a real mechanic to figure that one out too.
But he didn't need a scope, he just popped the cover and eyeballed stuff. And if you had put the Ford on a lift you could have done a visual inspection with a good shop light and ruled the visible parts of the harness out in 10 minutes.
This is the disconnect that often occurs and your entire routine is based on already having the answer in hand as was provided here. Prior to that you don't actually have any reason to put the car in the air and remove the ground effects so that the lower engine bay is even visible. (Oh, you didn't know that either did you?) What you did was move the finish line without having paid the dues to earn the insight that was necessary and that's exactly what has happened that has led to techs not being rewarded for doing the job the right way the first time. FWIW the wiring harness could have been damaged near any one of the other 12 modules that are, or could be on that data bus. That means the problem easily could have been inside any one of the doors. If that had been the answer provided you would then have said the same thing about just taking the door panel off and seeing the failure . But wait, we still have the problem that there wasn't proof that the harness was damaged until after I proved that was the case. Before that moment the car had all of the classic symptoms of a module such as the instrument cluster disrupting communication so maybe before you back guessed about putting the car in the air and looking at the harness you should have said to remove the instrument cluster from the circuit and inspect that harness first.
This all comes down to you (FWIW nobody did, not even me) had any idea where to look, nor why until after the critical details were gathered and then handed to you here by me. That information was collected using tools and routines and experience that you don't have and didn't even know were possible, let alone necessary. In the past our critics often played your game where they thought themselves fit to judge when they where themselves totally incompetent with the work that needed to be performed. The only difference here is we both know that you had zero chance of solving this no matter how much you pretend that someone could have somehow guessed right. BTW. That also goes back to the battery. Anyone who guessed that it could be bad would have gotten that correct, but it wasn't "the problem" and they would have easily been represented as having ripped the customer off by selling it.
Pretty good I thought.
(Rats, 12 hours into the new year and one of my resolutions is shot - try not to get under Doc's skin. Sorry.
And I think some decent software could have ID'd the wiring fault down to the exact wiring and even estimated the location to within a half inch. Really, if you have to run copper in a harsh environment, the wiring should be self-diagnosing itself all the time.
Cars are a pretty primitive collection of parts when you get right down to it.