Troubleshooting Dim, Pulsating Trailer Running Lights

Updated 07/30/2020 | Published 12/22/2014

Products Featured in This Question

Adapter 4 Pole to 7 Pole Vehicle End Trailer Connector

(600)

$31.18

Hook Probe Circuit Tester

(60)

$13.03

Question:

had a 7 pin connector added to and i have blinkers and brake lights and a very dim pulsating running lights on trailer,what to do now

asked by: Sam

Helpful Expert Reply:

It sounds like the problem is on the trailer wiring.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

However, you can test the pins of the 7-way with a circuit tester like # PTW2993 for voltage on the running light circuit to see if the voltage is on that circuit steady like it should be and not pulsating. The running light circuit will be in the 9:00 position of the connector when you are looking at the front of the connector.

I attached a couple FAQ articles on trailer wiring for you to check out as well.

expert reply by: Jameson C

click to enlarge

James S.

7/25/2020

I have a pulse at the truck on a 7 pin. pulse come through the running light circuit only when right blinker is on, works as it should with the left blinker on and everything works as it should when the lights are turned on for night driving.

Chris R.

7/30/2020

Somehow the right turn/brake light circuit is bleeding over to the running lights circuit. Inspect the 7-Way connector itself for any corrosion built up inside the pins that needs to be cleaned out. Sometimes rust can bridge two circuits together. Otherwise you'll want to check the wiring to see if you can find any exposed sections that might be shorting out to a nearby wire.