Turn Signals Reversed On Trailer Only When Running Lights Are On

Published 09/14/2017

Question:

with truck running lights off turn signals work fine,when you turn running lights on the turn signals work backwards??truck signal will be on left,trailer will be on right?all new lights and harness on trailer.

asked by: Jim

Expert Reply:

It sounds like there is a ground issue on the trailer, which can cause all kinds of strange things to happen with regards to the signal lights. The reason it is only showing itself when the running lights are on, is because of the additional load they are putting on the system. The current ground may be strong enough for the turn signals to activate properly by themselves, but when an additional function is activated, there is not enough power for everything to function properly.

I recommend checking that the main trailer connector ground and the grounds for all the lights are attached to clean, bare metal surfaces. Also check to make sure both the vehicle and trailer side connectors are free of dirt and corrosion, which can cause a short.

Lastly, ensure that all the trailer wiring is in good condition with no breaks or exposed copper that might be touching the trailer frame. I have included a wiring troubleshooting article that you might also find helpful.

expert reply by: Chris R