Awhile I got a second 1989 formula firebird with no engine or transmission because my first one had unibody issues. I switched the engine and transmission over to the new one but had to switch wiring harnesses computer and fuel pump over too since it was set up for tip and I had tbi. As soon as I switched it over it started up perfect but when I went to start again a few days later it stopped getting juice to 4 fuses on the fuse block what would cause this?

 

Welcome Aboard!

Which fuses are not getting power? It could be significant, since some of the fuse bussing is fed from fuse links and some from the ignition switch.

 

There's something else to consider:

How long had the '89 been sitting up with no engine and tranny? If it has been years, then there might be some bad contacts at the fuses in the fuse box. My Z28 sat up for 12 years, and when I got it going again, I had to pull all the fuses and clean the connections on the fuses and the fuse-holders. Even though these may not look corroded, they'll develop a "cold" contact much like a cold solder joint. It's a matter of taking some rubbing alcohol, some cotton swabs, and cleaning each fuse and holder. With mine, it would work at times then go intermittent on me. Kept doing it until I cleaned everything.

 

The engine compartment wiring harness and interior wiring harness both came out of the firebird I had been runnin since mine was tbi and the new one was setup for tpi there for I had to switch them and the computer over