How to Test Trailer Lights

Trailer lights are used to signal to other drivers that you are stopping, since your brake lights are not visible. They attach to your brake light wires and turn on when you touch the brakes. They are a very important feature to have on a trailer because some drivers have problems judging the distance of a trailer in front of them due to its low back end. So, when you attach a trailer, it is important to test the trailer lights.

Difficulty: Moderately Easy

Instructions

1. Attach your trailer lights to your brake lights as instructed by your trailer installation manual.

2. Depress your brake pedals and have someone stand behind the trailer and signal you when they come on. If they do come on, the lights are fine. If not, go to step 3.

3. Remove the trailer light connection harness from the brake light connector which is located on your trailer hitch. Depress the tab that holds them in place and simply pull the trailer light connection out.

4. Connect a voltage tester to the brake light connector. Attach the positive lead of the voltage connector to the brake light connector pin and the ground lead to the hitch. With the car turned on and the brakes depressed, read the voltage output on the meter. If it reads around 12 volts, the brake wires are fine. If not, there is a problem with your brake wiring.

5. Reconnect the trailer lights to the brake light connector. Then remove the trailer light cap and bulb. Connect the positive voltage meter lead to the trailer light socket and the ground to any piece of metal on the trailer Again, with the car turned on and the brake lights depressed, read the output on the voltage meter. If it registers 12 volts or more, the connection is fine. The problem resides with the trailer light bulbs. Replace them with new ones.

References

• Troubleshooting trailer wiring
• Forum post on trailer lights
• Trailer light tester

Resources

• Trailer light advice