Short-Term Solution to Connect Wiring on Semi to 7-Way on 5th Wheel Trailer

Question:

Hi there, I want to haul my 5th wheel about an hour away from where it is now. I bought a power service wire that I put a blade adapter that the 5ty wheel will plug into. So on the other end it has a adapter that will plug into truck power cord. Will this work?

asked by: Kurt

Expert Reply:

It sounds like you made your own version of our Trailer Connector Adapter # HM47425, which plugs into a 7-Way round connector like what is typically seen on semi-trucks and features a standard 7-Way Blade connector to plug into a trailer.

The issue is that the 7-Way round wiring on your semi features separate wires/circuits for the turn signals and brake light while on a trailer the turn signal and brake light circuits are combined. This means if you were to use your homemade adapter or the above-mentioned Pollak by itself, the only light function that would work correctly on the trailer is the turn signals.

To combine the circuits from your semi so that the brake and turn signal lights work correctly you will just need to add the Roadmaster Converter # RM-732 to your adapter. This will combine the separate wiring circuits so they are compatible with the trailer's wiring.

Just keep in mind though that this setup still won't be able to power brakes on the trailer. This would require a more complicated and permanent install. Due to the size of your tow vehicle and the short-term nature of your towing requirement this shouldn't be necessary.

expert reply by: Chris R