Running Lights Won't Work - Wiring Help Needed Please

I have one of these TEST ADAPTERS in my tool box to plug into the 7-WAy TRAILER CONNECTOR on the truck. This adapter has LED LIGHTS for each of the OUTPUTS coming from the truck side. If it doesn't work here then you know the problem is on the truck side. A great tool to have when having problems.

I got mine from ETRAILER but see them on AMAZON and I imagine some may available at auto parts stores.


ETRAILER.com has a lot of information including diagrams on their web site for everything trailer. Good place to go for info...

I am not aware of any fuses on the trailer side for any of the SAFETY lights or functions. I have found some WD40 sprayed into the 7-way socket before I plug into it helps some keeping the blades clean.

My truck does have fuses in one of the DC FUSE PANELs for the 7-way trailer connector. Also the key ignition has to be on for some of them as well...

I am just assuming the truck side connections for TRUCK CAMPERs are the same as used with RV Trailers here...

Roy Ken

First off, using standard colour codes, the brown wire is running lights.

Before you get much further though, your profile doesn't show what truck you have, Ford uses a double fuse setup. There's a second fuse box that has seep rate fuses for the trailer harness. If you have a dually, the marker lights on the rear fender flares are connected to the trailer harness so you can easily see that the trailer has no marker lights if you blow a fuse.

I'd start by testing that there's power coming out of the plug you're connecting the camper to.

it *should* be green for marker lights, white for ground, black for +12, red for left turn, brown for right turn.

my ford had a seprate fuse for the trailer running lites on the passenger side theres a fuse box number ten on my 2005 ford.

The more modern trailers like your '08 Lance are usually equipped with a good set of wires and lamp fixtures. Also there probably isn't a lot of oxidation.

Here's how I would troubleshoot the issues: Determine that the truck's harness has power at all the terminals and that the harness has continuity to ground. Here is a page of the different trailer electrical schedules----Harness schematics and wire color conventions. Next determine that the trailer's harness has all of the wires connected and in the right locations on the umbilical plug. PLug in trailer harness and observe for power at any of the unlit light fixtures. If you have power, there is a ground issue. If no power at the fixture, there is an open in the circuit. I'd venture a guess that 9 times out of ten, marker light issues are related to a faulty ground. Check real good for the ground wiring to the front fixtures and the first going back along the driver's side. That is where the chain wiring usually begins.

Good luck with the lights. Lance makes a fairly stout trailer so it is probably a minor issue.

Check to make sure you have a very good ground