Troubleshooting a 2007 Ford F-150 With Running Lights Not Working

Updated 10/23/2023 | Published 10/22/2023

Question:

Looking for some expert input/solutions.I’ve dug through multiple forums and can’t seem to find what I’m looking for. I have a 2007 f150 lariat. I have a combo 4pin with a 7pin next to it. Have towed my trailer several times all lights worked including the running lights off the 4 pin. Recently went to tow and suddenly the running lights no longer worked. Blinkers, brake lights still do. Have a rav4 with a 4 pin, hooked into that running lights on trailer work. Buddy hooked into his, again running lights on trailer worked. Wondered if my 4 pin was just bad so I bought a 7 to 4 pin adaptor with an indicator light 7 pin has a separate relay to it so in theory I figured if the wire for the 4 pin was bad it wouldn’t effect the 7pin. Popped that into the truck, connected to trailer no running lights. Not sure it is related, but in between towing with the f-150 and having the running lights work and going to use it again sometime later I had a serpentine belt snap and it ended up getting wrapped around some relays in the engine pay resulting in having to splice some wires. Looking for solutions on what could be going on. All lights work when the trailer is connected to other vehicles.

asked by: Joseph K

Expert Reply:

If you've already checked the trailer with other vehicles and all of the lights are working then the issue is for sure with your vehicle.

I'd recommend checking those relays the belt got wrapped up in, and checking those spliced wires as well because there's a really good chance that there is just some bad wiring involved.

I also recommend checking out the grounds and make sure they are attached tightly to a solid bare metal surface that isn't covered in rust.

expert reply by: Bryce D