Troubleshooting Both Trailer Turn Signals Coming On With Right Turn Signal

Updated 06/08/2021 | Published 06/05/2021

Question:

I have a 2004 Tacoma that has the HM43315 installed by someone before I bought it, the trailer lights when hooked up do not work properly. When the right turn signal is on both lights blink, when the left signal is on there is nothing. Brake and running lights are fine as well as hazard, I have used a led tester to eliminate the trailer and cleaned up the ground, what is wrong?

asked by: Steve

Expert Reply:

I would be happy to help.

First lets start with testing the vehicle side connector. Using the circuit tester you mentioned have a friend apply the brakes, then turn on the left turn signal, turn on the right turn signal, then turn on the head lights to activate the running lights while you are probing the connector.

If for one of these functions the connector does not have power, then check the engine bay fuse box for a blown or missing fuse.

Now since you said the brake lights work correctly that is a little odd as the brake lights and turn signals use the same wire, I recommend checking that the vehicle and trailer connectors do not have corrosion causing power to jump between the terminals.

Lastly check that the left tail light is properly grounded, and all of the connections are tight and secure.

If this does not fix the issue just let me know.

I included a link to a helpful article on wiring for you to take a look at.

expert reply by: Samuel C