Running Lights on Trailer Not Working After Installing New Lights With 2015 Toyota Tacoma

Question:

Hello, I bought a used boat and trailer 15 years old and decided to replace the wiring and all the lights, many of them not working, with new LED lights from eTrailer.com. I watched many of your online videos on both the parts and install procedures. All the lights were grounded to the frame, including the side marker lights. When I pulled the old wiring out of the trailer I discovered that when they installed the harness they cut and stripped the white ground wire and secured it to the underside of the trailer tongue. I did the same thing except I used a grinder to remove any paint or rust so I could get a solid ground to the boat frame. The stop and signal lights work but no running lights. I suppose it’s a bad ground but the two white wires out of the flat six plug new from trailer are securely grounded to the trailer tongue. The truck has a 7 pole RV style connector and the new wiring harness has a flat 4 so I have to use an adapter plug. I have a 2015 Toyota Tacoma and the dealer said that the wiring on the truck side was not the problem. Help! What do I do?

asked by: Dave B

Expert Reply:

Okay, so there's a few things you can do to troubleshoot why your running lights are not working after installing your new lights, and while a ground is likely the issue, let's just go ahead and be thorough here. While the dealer may have said the wiring on the truck wasn't the issue, you didn't mention fuses, so start with that; take a look at your owner's manual to locate any trailer fuses or relays and ensure they are all there and in working order.

If so, you'll need a circuit tester like # PTW2979 to verify the wiring is not the problem. Check the wiring going into your harness from your tail lights to see if those wires are carrying the correct signals, if not then the issue is with the vehicle wiring. If the signals going to your harness are okay, you'll need to test the signals coming out of the harness, and if they are correct then your issue is likely going to be with the trailer side wiring.

You will also want to check your 2015 Tacoma's 7-way for corrosion, which can be green or white in color. A build-up of corrosion can interfere with the signals getting through, so if you see any you will want to remove the corrosion.

Though you mentioned you have a good ground, you'll want to just do a quick double-check of that. Also, boat trailers sometimes have folding tongues, so if yours does and your ground is on the folding tongue, make sure your ground connection is on the main body of the trailer frame, behind the folding hinge.

I have added links below to a pair of help articles on trailer wiring, including a troubleshooting guide which I highly recommend taking a look at. Additionally, I also highly recommend using Dielectric Grease for Electrical Connectors # 11755 to help prevent any type of corrosion in your connector; using it will increase your connector's durability and extend its lifespan.

expert reply by: Kyle S