Lights Work on Trailer With One Vehicle But Not Other

Updated 07/24/2019 | Published 07/23/2019

Question:

I am trying to wire a 1975 Jayco travel trailer. We have all the wires ran appropriately, and when we connect the trailer to our 4runner, everything seems to work, but when we connect it to our F150, nothing seems to work unless my boyfriend connects a negative jumper cable from the bumper to the tongue of the trailer. We are assuming its a grounding issue, but is it on the truck or the trailer? We recently took the F150 to have the 7 way checked, because it was only partially working. When we got it back, all of the prongs light up on the circuit tester as they should, so we know the 7 way on the truck works. Where are we going wrong? Thanks in advance!

asked by: Paige

Expert Reply:

If the lights of your trailer work on your 4Runner but not your F-150 then the issue is on the truck; if it was the trailer then it wouldn't work with either vehicle. What I'm guessing is happening is that the pins on the 7-way of your F-150 are somewhat corroded. This can cause the connections to be problematic so you will want to check for that and clean them with some fine grit sandpaper.

You are also definitely always going to want to use Dielectric Grease for Electrical Connectors # 11755 to prevent any type of corrosion in your connectors in the future; using it will absolutely increase the durability and extend the lifespan of your connector.

expert reply by: Kyle S