I would check the battery cables first where it bolts to the block, then theres a ground strap that goes from the firewall to the block its near the end of the head. When we did the motor on mine we spent 3 weeks tracking down a electrical problem is was a broken soldered joint in the main engine wiring harness. Could be a number of things to I am sure one of the guru`s on here will have some more thoughts. I would bet it something under the hood not in the fuse box. Twenty year old wiring is allways fun and if you can't find anything obvious you may want to get the guy who changed it to fix it.