this might be a bitch, but it sounds like you have a bad wiring harness. question, where did you get the motor from? i built a 92 mustang with a 302 and the asshole who did the longblock apparently put a siezed motor in the car and i didnt know that until after i put it all together.i might be completely wrong, but im just trying to help. good luck.....

 

Alright start with all the grounds.. Run Jumper wires to the valve covers and the exhaust, Intake Fuse box. Then take the transistor box off of the fire wall and clean the firewall sometimes they get corroded and done get good enough ground.. do the same with the coil pack. if nothing else.. start checking fuses?