Using an Adapter to Connect a 7-Round to a 7-Flat RV Connector

Question:

I have an adapter for 7 round pin to 7 flat but when I hook up to a trailer the trucks brake lights come on and the trailer brakes lock up, I tried the on multiple trailers and other trucks and Im still having the issue The 7 round is connected to an 1994 freightliner FL70 and the 7 flat is to a 2013 Doolittle 8214-HD dump trailer

asked by: Ryan W

Expert Reply:

Sounds like the adapter you have is not the correct adapter for the OEM truck plug.

The 7-round to 7-flat trailer wiring adapters, like the Hopkins # HM47425, are wired to convert the typical 7-round wiring to the RV style 7-way with the flat pins. If your trucks plug wiring configuration is not wired like the standard 7-round, then when hooking the adapter up to your RV plug will cause the type of malfunction that that you are seeing.

I have attached a picture that shows what the commercial/agricultural style 7-round plug and connecter is typically. This configuration would be how the adapter plug will be set-up for to convert for the 7-way flat plug of your trailer. I recommend using a tester like # PTW2993 when finding the operation function of each pin on your truck's connecter.

If your trucks wiring is connector is wired correctly, then the adapter might be faulty and need to be replaced.

I have attached an article on troubleshooting brake controller and wiring issue for you to review.

expert reply by: Jared P