Troubleshooting Trailer Running Light Circuits Not Functioning on a 2004 Chevy Silverado 7-Way

Question:

I have a 2004 2500hd 4 door 4X4. I have no power to the brown wire, which should be marker lites on towed vehicle. I have tail lights working fine on P/U but nothng at plug-in. there is a maze of factory wires under the bed with what seems to be a junction bos mounted to a cross-member but is very hard to reach. there are both left and right signels and hot whire and ground at the trailer plug but no markers, the fuses are all ok. there is also a factory built-in loom that runs forward to the front of the bed for a camper type plug-in. any ideas where to start looking for a short or ground problem around that connection block on the frame. I dont see any broken wires.

asked by: Tom H

Expert Reply:

I would start troubleshooting at the connector itself. Take the connection apart and make sure there are no bent pins or corroded terminals that could cause the tail light function not to work.

Next, I would check the fuse block under the hood of the truck again. There should be a slot for a tow package fuse in there. Check the legend under the fuse block cover and you may find that this fuse is missing or that it has blown, and needs to be replaced. I know you said you checked there once, but GM fuses tend to blow easily so it can't hurt to try here again as this is the usual problem.

Aside from that all I could recommend would be to trace the running light circuit from the back of the connector looking for anything that could cause a short and fix as necessary.

I attached an FAQ on trailer wiring for you to check out as well.

expert reply by: Jameson C