yes they have wiring harnesses but its not really painless, i've had run in's with them before
of cource:P what wiring in the world is really plainless? hehe..wiring is the most dreaded part of working on a rig..lol..so many wires and so many chances of them being ground out...and the fried wire or wires could be any were..from the front to the back,,lol..i would rather rebuild a motor than have to deal with wiring..but the motor wont run with out wiring..so you have to do the dirty deed once and a while and find your problem...done alot of wiring..and i hate it every time
plus you ruing a early 70 rig..which means it will have alot of fusible links..bad thing about fusible links is there hard to find when there toast...only way to tell if there fried is to cutt the link out and check if the conection wire is gone...wiring is the devil!! hehe