I have a 78 gmc started out doing a simple engine swap then replaced floor boards and chance it over from ac to no ac with that some wiring needed changed, also took plug loose from firewall to route it above the brake booster where it belongs,..ends up I have no power to my radio or wiper motor...in the fuse box. Now I can take a jumper wire and make the wipers work with the switch but they go off randomly even if the switch is off usually just making one pass every 10-20 mins.

 

Well, that's strange.

did you change the engine size, and what year did the engine come out of and go into?