Just find an open spot in the fuse box and plug it in. Put an in line fuse and hook it up to a switch. It cant be much different than a set of fog lights or something.
I just turn the heater on defrost full blast and crack my window for a bit and it un fogs lickedy split...lol I didnt even know YJ's came with rear defrost.
91 Laredo, 4.0ho, TF999, Magnaflow exhaust, Yukon rear axles, Spartan Lockers, Posi locker, 3.5 inch springs, 1"MML, 1"BL, 1"shackles, trimmed fenders, raised flares, 35x13.50s.