Trailer brake light not working - FIXED

mrgreetis wrote:
. I tried the turn signals, tail lights, 4-way flashers and both filaments light with at least one of the combinations. Because of that I don’t think there is a problem with the socket wiring or the ground.

Unless you are looking at the bare bulb and comparing the brightness to the other side, you can't be sure that you don't have a ground problem because sometimes it "finds" a ground through the other hot wire and lights both filaments at the same time.

That often happens when the outside shield ground part of the socket gets corroded, or the notch where the ground nub on the bulb makes connection.