Left Brake Light on Trailer Does Not Work but All Other Lights are Working

Updated 10/25/2012 | Published 10/24/2012

Products Featured in This Question

Hopkins Endurance 4-Way Flat Trailer Wiring Harness - 20' Long

(58)

$25.97

Hook Probe Circuit Tester

(72)

$13.47

Question:

I have installed the Hopkins Endurance 4-way Flat Wiring Harness and cant get the brake light on the left side to work. I have a turn signal and clearance lights, but no brake light on the left side. I discovered the left side brake wasnt working when during the installation. The right side wasnt hooked up yet. Do I need both left and right brake lights hooked up simultaneously?

asked by: Jeff

Expert Reply:

The brake lights on a trailer are on separate circuits. There is one circuit for left turn and brake lights and another circuit for right turn and brake lights. If the turn signal is working on the left side but not the brake light, then it is most likely a bad ground connection. Ground problems normally show up when there is more load on a circuit like the constant 12 volt draw of the brake light.

Check the ground for the left side taillight. Many trailer lights ground through the mounting studs unless there is an obvious ground wire. In either case make sure the ground is attached to a clean and corrosion free bare metal surface. You will also want to check the main trailer connector ground and the pins on the vehicle and trailer side 4-Way connectors and make sure they are clean and free of corrosion.

You can also check the vehicle side connector with a circuit tester like # PTW2993 if needed. If the brake signals are not showing up on the vehicle 4-Way then there could be a problem with the wiring on the vehicle. I would need to know the year, make, and model of the vehicle to determine what the issue might be.

expert reply by: Michael H