Boat trailer lights work with the right turn but won't work with the left turn and when i turn on my lights

Question

Boat trailer lights work with the right turn but won't work with the left turn and when i turn on my lights

Answer 1

You have 2 bad connections, the left turn circuit and the tail light circuit. The ground is OK and the turn signal works to one side.  Check the lamps and the connections and the socket on the left side, also check the lamp on the right side. If you replace one socket and lamp, do the same on the other side. Boat trailers are notorious for corrosion in the lights, the wires also corrode over the years. Your best long term solution is to replace the 2 taillights and make new connections with clean wire, then waterproof the connections.

Answer 2

do you have a continuity tester??? it looks like an ice pick with a lite in the handle and a ground wire and clamp.