What to Check When the Lights on a Trailer are not Working Properly

Question:

2012 Toyota RAV4. Separate amber turn signals on vehicle, going to combined brake/turn signal on trailer. All lights work on vehicle when not plugged to trailer. All lights on vehicle work when trailer is connected. Trailer left signal light works with vehicle EXCEPT when using the brake so lighting the brakes. Hazard lights work on vehicle and trailer together. Left brake light on trailer doesn’t work but will flash as a signal. I’ve tried this with three separate trailer wiring systems with no change to the results. Any help please - when towing if I brake for a left turn I have no light on the trailer.

asked by: Jeff

Expert Reply:

As all the wiring harnesses available for a 2012 Toyota RAV4 are plug and play, I think it is actually something on the trailer that is causing the issue. I suggest checking all your ground connections to make sure one hasn't disconnected or become corroded. A bad ground can cause any number of weird things to happen, and this definitely sounds like what is going on. You will need to make sure everything is grounded to bare metal that is not aluminum. Each light should also have its own dedicated ground as well, especially if they are LED lights.

If this doesn't get the lights working properly, let me know and we can try something else.

expert reply by: Lazer S