Sounds to me that he may have accidently installed the wrong size fuse on the control circuit. People have a tendency to keep increasing the fuse size if they keep blowing. He probably has a short in the control circuit between the switch and the relay. That would explain the wire damaged in the area he mentioned. I would agree to pull the intire circuit out and start all over again. But I would add one thing. WIRE LOOM. If you go to your nearest HOME SUPPLY outlet and look in the electrical supplies, you will find 10' pieces for $2.00. Shouldn't take more than 3 bags. Cover every square inch of wire with loom before you install it. Then all you have to do is cut back what you do not need.
P.S. Never let the smoke out!