All Lights Flash on Trailer When Turn Signal is Used on a 2016 Ford F-350

Updated 08/23/2017 | Published 08/22/2017

Question:

My tow vehicle is a 2016 Ford F-350, crew cab, 6.7L King Ranch dually. I recently replaced all of the clearance and tail lights on my fifth wheel with led lights. When I do a walk around to make sure the lights are working properly before hitting the road I run into the following issue: With lights off tow vehicle and the 4 way flasher going all of the clearance lights and tail lights on the fifth wheel are flashing. With just the turn signal on either side both tail lights are blinking as well as the clearance lights. With lights on tow vehicle the turn signals and clearance lights on the trailer work properly. I have gone through and made sure that the pig tail wiring is correct and without corrosion on any of the wires. These issues do not come up when I tow my jet ski or lawn mower/garden trailer. Is there some kind of electrical load adapter that I need to install on the pig tail?

asked by: Vincent J

Expert Reply:

If your wiring all looks good, and your connectors do not have corrosion or debris in them then what you will want to do is check the wiring on your trailer with a separate 12V power source. What you can do is use the battery from your 2016 Ford F-350 and connect it to each pin individually on the 7-Way connect for your RV. If you are not getting the same issue when this is done, then there is most likely a ground issue on your F-350. You can verify this by testing the functions on your truck with a circuit tester # PTW2993.

Since your F-350 is a 2016 and it works just fine with other trailers, it will more than likely be a short or ground problem on your trailer side. You will want to check all of the grounds (including the individual ones for each light) and make sure that they are connected to a clean, bare metal ground. Even some paint can cause weird things to happen with wiring. If those all look good then inspect the wiring for any places where the wires have been bent, damaged, or have exposed wiring.

If all or your wiring looks good and the connector on your F-350 and your trailer work separately but do not work together you will want to take it into a shop so that they can physically inspect your setup.

expert reply by: Jon G