Rear left flasher not working, replace all bulbs without succes, then replace the complete harness thinking the socket might been burned but still not working. When I hook up my trailer, the light of trailer works fine (flasher, bresk etc)
Since the sognal goes to the trailer, where should I look at? Front flasher work perfectly.
Thanks.

What harness did you replace? Do you have a dvom?

The rear tail light complete harness (left side) that has 4 sockets attached to it and connected underneath the bed near the bumper. Ues I have a dvom

Are you missing the ground or power to the socket? Need to back trace.

Will get a look at the ground.

That'* a good place to start and is likely the area of concern.