Troubleshooting Left Turn/Brake Function of Trailer Wiring

Question:

I have wired up my 5 wire boat trailer wires to a 4 flat color for color with the running lights both to brown wire as described on this site and now my left turn signal doesnt work but the running lights do but before i had it this way the signals both worked and the running lights did not ? Do i have a weak ground or whats going on ?

asked by: John G

Expert Reply:

If you have a wishbone harness on your boat trailer that has two separate legs for the running lamp circuit running gown each side of the trailer, you'd connect those to the single brown running lamp circuit from the 4-pole.

Are you getting signal on the left turn/brake lamp pin on the 4-pole connector on the vehicle? A circuit tester like part # PTW2993 would come in handy at this point. If so, you'll want to trace the yellow left turn/brake lamp circuit from the trailer connector back to the trailer taillights. Look for loose connections or broken wires.

Check the ground connections as well, because a poor ground connection will make all kinds of weird things happen. Be sure the main ground on the trailer tongue is secure, and made to clean, bare metal. Make sure the left taillight assembly is properly grounded as well.

expert reply by: Mike L