Parts Needed to Re-Wire Trailer Brakes and 7-Way Harness

Question:

I have a new 2017 f-250 I pull a oil vac with It has two 6 lug axles under it When the truck is just plugged into The trailer and the toung is not on the ball My brakes work but when I latch the Toung to the ball the brakes quit working My trailer is equipped with a break away I just installed new breaks and drums New pig tails on both Truck and trailer I just can’t figure it out Thinking about re wiring the trailer What do you think

asked by: Spencer

Expert Reply:

It sounds like there could be a short on the trailer. Sometimes the physical connection between trailer coupler and hitch ball will complete the ground and let the trailer's electrical functions work even when the actual wired ground is no good. In your case the opposite is happening, which suggests that something is shorting to the trailer frame. When not coupled the short will have no effect since only the wiring is connecting the truck and trailer.

The issue could be caused by worn or cracked insulation, wiring rubbing against the trailer frame or even corrosion inside the male trailer-side connector.

Replacing the trailer wiring is the most likely fix. The linked article will be helpful. We offer handy junction box kits like # HS381-9000 that let you install a new 7-way plug and make the connections for each circuit on the trailer. You will need ring terminals like # 44-5310A to make the connections in the junction box; use butt connectors like # DW05745-10 to splice in any new brake wiring like part # 10-2-1.

expert reply by: Adam R