Years ago I had a trailer place make one for me but you can get adapters to go from 4 to 7 pin and the other way. I can make them in my sleep now.

 

I might be starting this project for myself. Does anyone know if there is 12 volt charging wiring in there that is active. I have a dump trailer i plan i using and i want to charge the battery when its hooked up. If the factory harness only has the electric brake wiring then i might have to go aftermarket . Thoughts or info let me know thanks.

 

If you want to spend the money, U-Haul has everything you need to install a flat 4-wire plug. My 2000 XJ came with the standard trailer tow package, but the lighting module was an epoxy-molded deal with embedded solid state relays. This is what shorted out and burnt up my harness! IDK if this was factory or aftermarket, but it doesn't exist anymore! I did find a single pin connector with a blue wire that was dead and I couldn't trace, so now I know it's for the electric brakes. To tell you how badly rusted my XJ is, I backed into a high concrete curb and broke off the tow hitch!

When I was towing my camp trailer with my Chevy truck, the one thing I always wanted was reverse lights on the trailer! It would have made setting up at night so much easier! The truck had a 7-pin connector with a hot battery wire that was only live with the ignition on. That was used to top off the trailer battery. IDK since I bought the truck already set up. I pulled a 15 ft travel trailer with electric brakes and a manual brake controller on the dash.