How to Test Dim Trailer Lights After Connecting 4 Pole Harness

Question:

When i hook up my trailer the lights are super dim and turn signals blink very low when my headlights and all are on any help?

asked by: Dalton

Expert Reply:

Not to worry, this is a common issue, and I will be happy to help you get this issue working. Most likely it's a weak ground for the trailer lighting assemblies or for the entire trailer itself. Try improving the grounds of each assembly by ensuring they are connected to a clean metal surface to see if that will help. Also make sure that the main ground from the trailer wiring is making a solid connection to the trailer frame. The lights usually ground through the mounting studs. If there is any dirt, corrosion, or rust it could cause a bad connection. You will also want to check where the light bracket mounts to the trailer. I have included a video below on testing for a ground.

Also use a circuit tester like # PTW2993 to check the trailer connector for proper voltage coming out of the connector. If you are not getting the proper voltage, then we will check further in the wiring. I have attached a video that shows how this process is done.

If you are using an aftermarket wiring harness like # C59496, then I would move to testing the converter box. Start by testing for voltage on the wires going into the converter box, then test the wires coming out of the box going to the trailer connector. If the voltage going in is good and the voltage going out is not, then the converter box is bad, and the harness will need to be replaced.

If you have a factory tow package, ensure the trailer connector pins do not have any corrosion on them. Also check the wiring on your trailer for any places where it may be corroded, bent, exposed, or damaged. You can use 16 Gauge Wire # 16-1-1 and Butt Connectors # DW05744-5 to replace any wiring that needs to be replaced.

To test the trailer side, you might even try powering the trailer lights with a 12-volt battery to see if that makes it light up brighter as a way to test it. If you ground the battery to the trailer frame using a wire from the negative post to the frame. You can touch each of the trailer light wires to the post to check for full brightness. If the lights remain dim, then the issue is on the trailer side and there could be a wiring or short issue. If it does light properly the issue is coming from the tow vehicle.

If you have any issues with this process, feel free to contact me for assistance.