How To Wire A Seven Pin Trailer Plug. These are the type of plugs used on car trailers and caravans. I finally decided to dissect mine to find out.
Now probe the vehicle wiring to find out which wire leading to the taillights is hot. I'll refer to wire color and gauge to make following along easier. The black post is for the auxiliary power, the silver one is used for hooking up electric brakes for a trailer.
The seven pin plug on our travel trailer was not staying plugged into the truck very well and the breakaway switch had a worn wire.
One benefit is that no one will be able to borrow my trailer because mine has "custom wiring".
And the trailer plug on the back of your truck doesn't remotely match the one on the trailer. So here I have an older trailer which needed some work, along with re-wiring the lights. There is a lot wiring that you have to tie into your truck's wiring harness, but it is easier to do than it seems.