This old link from the Studebaker Club is a copy of the original instructions.
http://www.studebakerclubs.com/North.../Overdrive.pdf
Page 7 has a basic wiring diagram that can be used for all of the Borg Warner systems. The only difference from 1950/E51 is the delete of the rail lockout switch. It was considered redundant so its use was discontinued for most of the 1951 model year and on for Ford products. All the other components were used up till Ford quit offering the T85N/R11 transmissions.
Solenoid wiring should have a relatively large gauge wire even with 12-volt. The control wires can likely be 18 gauge but the power from the battery to the relay and the relay to the solenoid should be around 14 gauge. It take a lot of amps to engage the shift solenoid.
I always warn folks new to the Borg Warner overdrive to be careful when parking on hills. Either lock the OD out manually with the cable or shift the transmission into reverse to make sure it is locked out so it won't try to roll. There have been a lot of runaway vehicles with these type transmissions over the years.