Trailer Turn Signal and Brake Lights Dont Work But Running Lights Do  

Question:

Helpful Expert Reply:

Even if you have checked all of the connection points and fuses, there could still be a short in your wiring somewhere along the line. If you put proper protection on your soldering, the best protection would be using Heat-Shrinkable Tubing # DW05449 with Electrical Tape wrapped around the places that you soldered, then your splices should be okay. Otherwise the connections could jar loose, or in cold conditions they could become brittle and ineffective.

If your connections look good, then what you will want to do next is test the connection on your vehicle end to make sure that you have signal strength getting to your trailer. This will tell us if the problem is on the vehicle or on the trailer. You will also want to make sure the ground connection on the trailer doesn't have rust or corrosion, which can cause a faulty ground. If you are using the 7-Pole to 4-Pole Adapter # 37385 that you referenced, I have a few different options to help you test it.

Since you will be testing not only the wiring harnesses for your tow vehicle, but possibly the wiring on your trailer as well, I recommend using the Draw-Tite Circuit Tester Kit # PTW2993 to do this with. This kit is great for testing harnesses because it features a light and a beeping sound when it receives a signal. This can make testing easier if you don't have an extra set of hands to help you.

If you test the 7-way harness on your vehicle side and it is functioning properly, we can move on to testing the trailer wiring. The Tester Kit has a hook that is included that allows you to pierce a tiny hole into your wiring to see if certain locations are getting power. You can simply move along your trailer wiring until you find where the signal stops. If you need some additional wiring, we off Deka 10 Guage Wire # 10-1-1 that will work for you.

I have attached some demonstration videos for you as well.

expert reply by: Jon G

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