Troubleshooting Trailer Wiring When Running Lights Do Not Work

Updated 03/27/2015 | Published 03/26/2015

Products Featured in This Question

4-Pole Trailer End Connector

(39)

$7.47

Hook Probe Circuit Tester

(60)

$12.27

Question:

Ive got a flat 5 connector to a boat trailer. Everything works, right left signals, brakes, emergency but no running lights. All the functions above work with the truck lights on also, but no running lights. Ive checked and bridged across all the trailer ground connections and all connections on the vehicle side are showing voltage including brown. Just cant use the trailer at night. I purchased a new 24inch 5 flat extention from you last week and it is installed. old one was shot. Needed. . . but did not help.

asked by: Mike M

Expert Reply:

It sounds like there is a ground wire issue on your trailer. Since you said you checked the vehicle harness, and it checks out we can rule that out as the issue.

You will want to use a circuit tester like part # PTW2993 and check the wires coming out of the trailer connector when plugged into the vehicle. Make sure the pin for the ground on the trailer connector is not corroded or bent. Check the lights and make sure the ground wires are securely fastened to a clean bare metal surface, and that none are broken.

expert reply by: Jeffrey L