Troubleshooting Trailer Lights Malfunctioning When Cap is Closed on 7-Way

Question:

18ft trailer. When I plug trailer to truck the all lights work until the lid cover latches over the plug then the lights go out. so, When plugged 3/4 of they way in all works, when completely inserted all lights go out. Im puzzled. what ya think.??

asked by: Jayson M

Expert Reply:

Sounds like you have the classic loose wire/loose ground problem on your connection. When you let the lid close on the 7-Way it places more pressure on it which then shifts the connection points around just enough that things start to malfunction.

What you'll want to do is check your grounds and make sure they are completely secured to a clean, bare-metal surface and then take the covers off of your 7-Way connector and socket to check the connections to the wiring itself. Troubleshooting wiring can be tedious but if you're slow and methodic with your approach it's usually not hard. If you have another trailer with a 7-Way handy you can try to recreate this with that trailer and that might let you know if your initial trailer or your truck is where the problem lies.

I'm linking videos of the 7-Way connectors # PK12706 and # PK12-707E being installed so you can see what you'll be looking for as far as the connections go. I'm also attaching a link to a helpful article about troubleshooting wiring for you to check out.

expert reply by: Jon G