stealman1

03 model truck
Everything on the truck works and Everything works on the trailer but the tail lights-running lights. Its the truck not the trailer. I have tried two trailers and have the same problem and I have checked the 7 pin plug with a volt meter and get no power for the tail light circuit. Where do I start to find the problem? It doesn't look like there is a fuse? If the truck tail lights work does that mean that the problem is between the tail lights and the 7 pin plug?
Please help

jumper

There is a separate fuse for the trailer tail lights. It's under the hood in the large driver's side fuse panel. At least there is in my 2005. I still don't have a working horn because I borrowed that fuse when the tail light fuse blew, 10amp as I recall.

It *might* be fuse #33 if I interpret the wiring diagram correctly. I don't have access to the truck right now.

El Borrego

If it's not a fuse you will need someone good with vehicle electrical system to check the fuse buss under the hood. I had a similar problem with trailer on one side. Come to find out it was the buss shorted out, I think from the factory as I had never used a trailer prior to finding out it didn't work. The buss is expensive, about $800 installed. It wasn't under the warranty either. Truck had 100K and was 2 years old. I asked about using a spare slot in the buss and was told it might and might not work. Seems computer on truck knows what is connected to each fuse. Mech. said it may crank a few times and then it wouldn't crank again because of the computer recognition.

SOhappy

Common problem, if it's not fuses then try this:

https://www.dieseltruckresource.com/...light=modulite

Cheap, easy, relatively painless. Fix it and be done.

(maybe a sticky?)

dieselfreak21

There is a fuse. It is either 33 or 23 slot. It is a 20 amp. Replaced several of them while figuring out the short in my rv lights. It is in the box under the hood on the drivers side. When you take the cover off there is diagram and list of what fuse does what. I don't think the 03 has the bus problems as there isn't supposed to be one. Don't quote me though.