I am Running the - Cranks OK, but No Start Checklist - Help Please

So, I got to #5 - B: checking injector for 12V with key in the on position, with my meter reading absolutely nothing (as in nothing at all, my test light detects no electric current at all). Strange thing is when I have the key in the off position my injectors read 9ish volts. I pulled the injector harness off at the salt/pepper connector, checked for continuity and cleaned up both sides of the connectors (which actually got me to reading 9ish volts, whereas before it was 5ish volts).

Checking the female side of the "pepper" connector, with key on, my test light reads nothing, won't even come on. With key off my test light reads 9ish volts. Checking the "salt" side of the connector is same except it reads 12ish volts. I've pulled the computer and cleaned up its connectors and everything inside looks as good as I can tell, which I also found out it was refurbished or replaced in 2014 via a little sticker on the case. I also replaced the EEC relay and checked wiring around the computer. Is it a bad computer?

I'm wondering if anyone has had any of these symptoms before or have any idea what I might be dealing with here. It seems like the injector harness is fine, with the main issue being the "pepper" side to the computer/relay isn't getting 12V. She's an 89 with a 5.0 and 5-speed TR3550. I love her and want to zoom around in her! But alas, she crapped out end of last season and I've been chasing gremlins since then.

Thanks for the thread help Noobz.

She crapped out end of season last year after I had repaired and replaced a bunch of stuff that needed attention. New gas tank and everything that comes with that (pump, sending unit, filter, etc.). Put on some longtube headers because the front end had exhaust leaks all over and figured I'd get some fancy longboys to replace the factory ones. Did the engine mounts, starter, coil, plugs, and wires while I was at it. She was running fine after doing all this stuff and she zoomed around swimmingly.

End of season I pulled off the upper intake to clean some stuff and just take inventory of things and what I wanted to do next. Soaked the upper intake which had been painted black and made to look like a Holley (it even had a Holley plate, which after I removed only then discovered it was a stock intake!). Scrubbed the upper intake out and in the process of just soaking it all the paint started to slough off - so I scrubbed all that off. I reinstall the intake and drive her around for a few days until, one morning, I go start her up and she starts... but after a few seconds idles out and dies. I try and start her again with just cranking. A day or so later I try starting her again and she fires up! For about 3 seconds before idling out and dies.

It as the end of the season and it was getting cold so I couldn't work on her - so I covered her and put her in my carport and there she sat. Until a few weeks ago - with a host of new parts. So I put in a new Edelbrock Performer RPM II intake, new distributor, throttle body, fuel injectors, and related bits - and have been trying to get her started since then. She is timed correctly, making spark at the coil and plugs, fuel at the rails... and we're at we are now with my first post.

This has been my Tedtalk. Sorry for the length!