Are there any other lights that are inoperative such as the parking lights outside of the truck, or the overhead console or the radio? The parking light circuit sends power to the rheostat in the headlight switch to control the dash light intensity. So if the parking lights are out start by checking fuse #18. If the parking lights work check fuse 13 for power as you change the rheostat position with the parking lights on. If that is OK and the overhead console does light up then you are headed towards the instrument cluster lamps themselves or their circuit.
Then you'll be pulling the instrument cluster confirming power to pin #1 connector A orange wire. From there you will be looking at the bulbs themselves in the cluster.
So the parking lights don't work. Correct? The parking light circuit provides power back to the headlight switch for the instrument cluster lights as mentioned earlier. Check fuse #18 and make sure it is good, and has power to it when the headlights are turned on. Even basic circuits such as this demand a disciplined approach when diagnosing a failure. There are no silver bullets and any tips given to look at a particular common trouble area still require some pinpoint testing to confirm if the tip is valid "this time". No-one can just tell you what is wrong. The best someone can do is to tell you how to figure it out but only if you follow through and make the checks that are required.
Answers
If the parking lights work check fuse 13 for power as you change the rheostat position with the parking lights on. If that is OK and the overhead console does light up then you are headed towards the instrument cluster lamps themselves or their circuit.