Attempting to Troubleshoot 2016 Ford F-150 Bulb Fault on Trailer

Question:

I saw a similar post - I have the same issue. My vehicle came with the tow-package which includes both the round and flat connectors. I thought the wiring might be an issue with my camper but when I towed my utility trailer with brand new wiring, I continued to see the bulb fault on my left turn. The camper uses the round plug, the utility trailer the flat. I took it to the dealership and they said its hard to troubleshoot and spent a day on it with no results. I made another appointment this next week to see if they can continue to search, but they were not optimistic. Ive used anti-corrosion lube on the connectors, cleaned them, scrubbed the grounds and this seems to only appear when I turn. Plenty of slack on connector and wiggling it does not trigger this to happen. Any ideas on how I might diagnose this - I have a week before I have to take it in and would really like to narrow down the issue to the truck or both trailers have issues which I find hard to believe since I did not have similar issue with other town vehicle.

asked by: John W

Expert Reply:

There is a way to attempt to narrow down whether the wiring issue is on the truck side or the trailer side, which I can help you with. In order to determine the specific problem you will need to purchase a circuit tester if you do not have one - the very handy Cordless Circuit Tester # PTW2979 would be my strong recommendation due to how easy it is to use - and test the connector on your vehicle after disconnecting it from your trailer.

Check the wiring going into your harness from your tail lights to see if those wires are carrying the correct signals, if not then the issue is with the vehicle wiring. If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring.

This should at least give you a place to start to try and see if is the trailer or truck side. I've also added a link to a help article on wiring troubleshooting which I highly recommend looking at.

expert reply by: Kyle S