How to Test a Trailer Blinker That is Not Working

Question:

The trailer lights work except the left side blinker only works when I tap the tail light, when I return it wont work unless I repeat. right side works and running lights work. I had a trailer shop check it out and they tested the trailer unconnected to the vehicle and it checked out fine????

asked by: Richard V

Expert Reply:

This sounds like either a ground issue or a wiring harness that is going bad. This will also depend on if you have a factory or aftermarket wiring harness installed.

A bad ground can do all sorts of weird things. You will need to check to make sure the white wire on the back of your vehicles wiring harness has a good, solid connection to bare metal. These can become corroded over time causing something like this to happen. This is only applicable on an aftermarket harness though as a factory ground is usually integrated somewhere inside the vehicle.

If the ground looks good, or if it is a factory harness, you will need to check the port that has the yellow wire going to it on a 4 flat, or the 9 o'clock position on a 7 way. If you are not getting pulsing power when the blinker is engaged, then the harness will need to be replaced. I would typically tell you to check your fuses, but since you are getting the blinker after the brake pedal is pressed, it isn't a fuse that is out.

expert reply by: Lazer S