Troubleshooting Trailer Running Lights Not Working When Hooked Up to Truck

Question:

Just trying to figure out all the fuses and relays I need to change. I already changed the #42 30a fuse and the #55 relay but that didnt help. My trailer plugs are all brand new. Had someone inadvertently stick their tester in my hook up and it took my running lights out. Thank you for any help.

asked by: Jason K

Expert Reply:

The running lights can go by a few different names in the manual; running, tail, or even park. It looks like the number 22 slot uses a 15A fuse for your park lamps that you can check out, but that would be for your 2010 F-350 lights.

If those lights are okay and it's only your trailer lighting that's seeing the issue then what I recommend doing is using a circuit tester like # PTW2979 to test the running light pin on the socket for your F-350. If that is showing power with your headlights on then we know that the issue is on your trailer and is probably a shorted wire or bad ground. If you don't get a signal on your truck's socket then you probably have some damaged wiring or a bad ground on your truck side that you need to check out since you've already changed out the related fuse and relay.

Attached are photos showing where the running light pin will be on your truck socket, as well as an article on troubleshooting wiring that you might find helpful.

expert reply by: Jon G