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Chevy Silverado and GMC Sierra Trailer and Towing Questions



  • i just recently bought a 1500 sierra with a factory installed tow package and wnat put hook up electric brakes for towing. i have read that all i need to do is plup in the controller in under the dash which i found. i know other people that have done this and needed to get a resetable circuit breaker for it. do i need to get one or is it all set to go. and if so where is it? is it a fuse or a circuit breaker. also anyone know what the wiring diagram is on the factory 7 plug for the trailer? are one of the slot for a constant 12v accewsory? do i need a fuse for it or anything else to hook it up. cause i checked with a volt meter and i couldn't seem to find one. any help would be appreciated
  • Looking to buy used truck, but not sure if it strong enough for what I have. I tow my trailer with a F150 and I hate knowing it is too small for my trailer. 10,000 lb. trailers are heavy, do I need to worry with a 6.0L HD?
  • Quote: I have a 2005 2500HD with the Duramax, with the same problem of no aux power in the trailer connector. I checked in the manual and it says DO NOT install a fuse in the STUD 1 location on vehicles equipped with the diesel or 2 batteries..... I have both. Any ideas?


    I spent quite some time today going through my 2003 GMC 2500HD truck trying to get an answer to this very question. And I think I've figured out why...

    My truck has the plow prep package and the towing prep package. It also has dual batteries. I found that part of my dual battery setup connects an extra wire directly to stud 1 (not the fuse location, the actual stud below the plastic cover) that gives it power when the key is in the "on" position. This effectively makes stud 1 a switched power source.

    If one were to put a fuse in the stud 1 spot, then it would make the trailer wire live all the time, but it would also feed power back into some portion of the dual battery setup as well, which I would think is bad... There has to be a reason for the switched source, and I assume that GM had a reason for making stud 1 switch that way.

    I'm assuming this power feedback would cause some other things that are expected to be off when the key is off to stay on all the time...

    And, if you think about it, it makes a certain amount of sense. Why would you want to charge the trailer battery without the truck running? You'd want the power switched so that your trailer can't drain your truck's batteries... However, you'd want to run off of the truck's power if and only if there's an "unlimited" source there. You wouldn't want to drain the truck's battery by running your trailer off just the truck battery. But running the trailer off the truck's alternator? That's a better idea. This adds more credence to the idea of only powering it when the truck is in the "on" position, because 99.9% of the time when the truck is in the "on" position, it's running...

    I think if you checked your 12v wire in the trailer connector, you'll likely find that it is dead when the key is in the "off" or "accessory" positions, but is live when the key is in the "on" position... At least, I did...

    Hope this helps.

  • pantera123, do you have a dual battery setup? Have you checked if there's power to the 12v constant when the key is in the "on" position? My 2003 2500HD has dual batteries, and the 12v wire is switched on only when the key is in the "on" position.

    If you DO NOT have dual batteries, then you have to put a fuse in "Stud 1" position in the fuse box under the hood. If you do have the dual battery setup, the trailer 12v constant *should* be switched without the fuse...
  • I think you hooked up the wrong wire.

    the 40 amp fuse in the Stud1 connector should go to the solid red wire (which was taped under the master cylinder?), which is the 12v constant to the trailer harness.

    What you're looking for is a Red/Black (I think that's the right colors) wire that connects to stud 2. I believe that wire is taped between the underhood fuse panel and the inside fender wall...

    I get the locations of the two confused, because both are already hooked up on my truck. But one wire is taped under the master cylinder, and one is taped between the underhood fuse panel and the left inner fender wall. They are two different wires, with two different sized ends, and each will only properly fit on one stud or the other. I do know for a fact that the stud-1 wire is the trailer 12v constant wire, and the brake controller is the one that connects to stud-2...

    Hope this helps...
  • countryboy34, First off, the 7 pin plug at the back of the truck is standardized. It won't change from truck to truck. Looking into the plug from the back of the truck, the wiring should be as follows: (Also, on my 2003, my stock plastic cover over the jack itself also shows the wiring diagram as well - if you look closely, yours might as well)


    You should note that in this picture, the wire "colors" are incorrect, but their positions are correct. This is standard 7 pin wiring. The Auxiliary pin in the middle is setup from the factory as the reverse light lead.

    There are two wires under your hood that need to be hooked up. One of them powers the 12v port on the trailer connector, and the other is the power lead for the electric brake harness under the dash. I forget which wire is where, but one of them is taped on the firewall under the master cylinder and the other is taped between the underhood fuse panel and the inner fender. They're two different sized wires, with different sized ends. One of them connects to "stud 1" and the other connects to "stud 2". The ends are sized to properly fit on only one of the studs each, so you can't mess it up... Finally, be sure that there is a 40a fuse in the "stud 1" location, and a 30a fuse in the "stud 2" location.

    for a 2004, you should be pretty much plug-and-play to connect the electric brake controller in the cab. But once it's hooked up, verify VERIFY VERIFY that all lights work properly on the trailer, and that the trailer brakes don't lock up when you turn on the headlights. Some Chevy/GMC harnesses under the dash are incorrect and lock up the trailer brakes when the headlights are turned on. If this happens to you, I hear it's just cutting and switching two wires around, but I don't have the details on that...

    So, it's definitely not going to be a 5 minute install, but if you spend some time researching the points I've made here before you go hooking up wires, it can be a 30 minute install including testing...

    Hope this helps..
  • cam77cam77 Posts: 1
    I have been trying to determine whether I can tow more than the 6700 lbs listed in my owners manual. I purchased a new '09 GMC Sierra 1500 extended cab with the standard bed. It has the 5.3 LMG engine with flex fuel capability, it's coupled to a 4 speed auto, and the rear gear ratio is 3.42 with the locking rear differential. It was upgraded with the heavy duty towing package, the HD trans cooler, and has the Z71, and z82 packages. This will be used to tow a lightweight fifth wheel. I contacted GMC and they couldn't help. I have looked everywhere and can't determine whether the packages improved the payload or just added a safety factor to towing. Any ideas?

  • My 2007 Sierra tows up to its rated load well, and may comment on its ability to haul beyond its rating when the truck has surpassed its warranty....Wish the truck was available with a manual trans. Equipped with the tow pack, trans cooler, snow plow prep(and I plow with the truck), 4 speed auto, 3.42 auto lock diff., 4.8L V8. I added an electric brake controller to this truck, and feel it's added a margin of safety.
  • I pull a 3000lb 20 foot bass boat with my 2001 with a 5.3 4x4. It pulls very well, but, like everything else you have to stop it. Any vehicle will yank a trailer, but if you can not get it to stop you are in trouble. When I see a suggested towing capacity of a vehicle I always picture in my head the size of the trailer they are talking about. For example, a 7,000 boat might be a 25 foot cabin cruiser on a 3 axle trailer. Can you picture yourself driving a Grand Cherokee Jeep or Chevy Trailblazer pulling this? And then safely stoppinig it? Not me, I always go for the over-kill.

    Another item that is of the utmost importance is the hitch and ball rating as well. Seen too many people bolt on a hitch to the bumper and then try and pull huge trailers.
  • I have a 2002 HD with a trailer package. All of a sudden the trailer lights are acting up. The turn signals work fine by themselves. When I turn on the lights or apply the brakes, the opposite turn signal blinks and the corner lights come on. Any thoughts???
  • Check your ground wire. Most commonly this comes loose at the trailer end where the installer or manufacturer ran a short piece of wire (typically white or green) from the multi plug of your truck to the chassis of your trailer. If it isn't kept clean and free of corrosion, it will often get gunked up to the point of loosing conductibility. You can usually test this by loosening the screw a touch, then shifting the terminal side to side to scrape away the corrosion. It is also possible that he copper wire has corroded through and needs to be replaced. Anyhow, usually if your lights still work, but work "erratically", it's due to the ground. When your main chassis ground goes, then the lights find a different path to ground, which is usually another light that isn't being used, or isn't supposed to be on at that particular point in time, causing all sorts of craziness. Good luck!
  • Thanks for the info. I forgot to mention the same thing happens on another trailer, so my guess would be there is a problem with teh ground on the truck, correct? It's a factory installed harness, any idea where it might be grounded?
  • No, not right off. If the weather clears up today, I'll crawl under and see if I can figure it out on my truck. Usually the ground wires get screwed to the chassis somewhere near each and every device or harness. There are some exceptions, but very few. So I would start by following the harness wire bundle a short ways to see if one wire branches out and screws to the chassis. It is even possible that the harness itself grounds to chassis. Another option, if all else fails, would be to add a new ground wire where one end screws to the truck frame and the other end screws to the trailer frame, with some sort of quick disconnect in the middle. Not ideal, but if in a pinch, and you can't find the problem in the truck that would allow you to be legal. Also, minus the quick disconnect, you could use it for troubleshooting to see double check if it is indeed a ground issue. I'll post again if I come up with any more information on the harness and ground.
  • Awesome! I'll see what I can find.
  • artm7artm7 Posts: 1
    I just bought a 2006 Silverado 3500 2WD with trailer towing package and am preparing it for a truck camper that we also just bought. The truck has the factory harness as well as a plug in the box for a goose neck/fifth wheel. I built a extention cable to reach the front of the box for the camper plug. In testing it(both turn signals worked fine) I accidently short the tailight wire to ground. Now all plugs, including the factory plug under the bumper, are 100% dead.

    Where is the fuse that controls the trailer harness???? I've checked all fuse blocks and can't find anything. Is there an inline somewhere?


  • On my 2002 1500HD all the trailer fuses are under the hood in a box on the drivers side fenderwell.
  • On my 2001 chey 2500 4x4 the fuses are either in a box under the hood on the drivers side or at the very left end of the dash, on the end cap. Open the drivers door and look at the end of the dash.
  • I set up my 2001 chevy 2500 4x4 SB Extended cab 6.0 V8 to haul a 38 foot 5th wheel from Sacramento to San Felipe Baja Mexico. It did a good job for me, but I may have overloaded the truck, as 4 months later, both side of the frame broke in two pieces. It broke right where the frame changes from a channel steel frame to a "C" frame.

    I just had it welded and reinforced and it $ cost $800. I still love this truck and should have bought an "HD". It has a bigger frame. My next truck will be a used 2500 HD duramax 6.6 with allison trans.

    Can anyone suggest which year has the least amount of problems with the engine and trans? 2004, 2005, 2006 ?
  • brad03brad03 Posts: 2
    Hello. I'm having problems with power to right side tail lights of my fifth wheel. It worked great then suddenly just quit. I imagine the problem is from the factory wiring to the ( 6or 7way plug??) Suggestions of possible causes Please. Is the trailer power system wired ( fused) seperate from the truck. I've heard a truck tail light for instance, can be out, but the trailer light for the same side can still be working? This is all very new to me.
    My truck is a 2007 GMC Classic.

    Thanks to All Brad03.
  • brad03brad03 Posts: 2
    Hey,....My 2007 GMC Classic has been a super truck. Dmax/Allison 6.6 turbo gotta be one of the best combos made. I haul a 30 foot fifth up and down hills all day @ 70mph, and that truck just won't quit. Ran through KT yesterday and there isn't a hill on I71 or I65 that will slow it down. Gotta Love It
  • I just bought a 2009 GMC Sierra 2500HD Duramax. It is significantly higher than the 2000 Ford F250 Super Duty that it replaced. GM now makes 4X2s and 4X4s the same height. Onlyh issue is, I now have only a 2" gap between the top of the cargo bed and bottom of fifth wheel, which won't work. I don't know what gap to shoot for. Does anybody in this forrm?

    What have other people buying 2007-2009 Chevrolet Silverado/GMC Sierra trucks done?
    Thanks. :confuse:
  • catamcatam Posts: 331
    As much as possible and still maintain a level ride on your trailer.
    The easiest fix for your problem would probably be to "flip" the axles on your trailer.

    I personally wouldn't tow the 5th wheel around without at least 8 inches of gap. If you never tow it anywhere that has a significant road pitch transition (ie Off Road), you might get away with less.
  • I want to tow my1994 Silverado behind my RV. Instructions I have found say; transmission in park, transfer case in neutral, and remove the fuse. What fuse might that be and where is it located? Thanks, azjerry
  • Bought a 2004 2500 HD and moved my brake controller and plug out of my 2002 1500 HD and am getting some really weird stuff. Can anyone tell me if the wiring harness changed between 2002 and 2004?
  • I have a 2008 Sierra with 5.3l and 3.42 gear ratio. I understand that if I had the 3.73 gear my tow rating would be 7700lbs, 1000lbs more. I am planning on buying a travel trailer this spring and the extra pulling power would give me more options for a purchase (the trailers I like weigh about 6000lbs empty). How should I go about doing this, and about how much would it cost? If I have my dealer do it, would I keep my warranty?
  • obyoneobyone Posts: 8,054
    The part will cost about $500. Not sure how much it would cost to install it as it varies depending on whether a dealer or trans shop does it. You would also need to have the computer calibrated for the new gear.
  • jtd3jtd3 Posts: 1
    I am going to be installing a trailer control in my 2005 silverado 1500. How do I know if the plug under the dash is hooked up and ready to go
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