Have a boat trailer (about 3,400 lbs. ) that I thought would be good to haul around to aid in engine break-in (though suspect I'll hardly feel it when towing). It has disc brakes that are activated by a collar moving back and forth and operating a master cylinder at the front of the trailer. There is an electrical solonoid which cuts off the trailer brakes so it can be backed up. Instructions for hooking the cut off (two wires) to the tow vehicle indicate that one wire should be attached to the back up light and one to ground. Leads on the cut off are about 30' long. If anyone has a wiring diagram or has already hooked one of these up, where is the best place to attach the two wires? Do the back up light wires cross the back of the truck at the rear bumper?