The car is a 88 gta
So I put a tpi stand alone system in the car.only pulled out the engine harness an ecm left all the other factory wires in to use .crazy problem I am having is when the key is turned to the run position the radio aftermarket gauges an dash power go out an come back on after releasing the key!car will start run an everything works as it should.for the life of me I can’t figure this out

 

Normal instrument panel, or digital instrument panel?

With normal instrument panel, the ECM fuse and GAGES fuse are powered by the same wire, active in both Run and Crank key switch positions. All the gauges and warning lights and everything should work with key in Run and Crank.

Digital instrument panel appears to be different. I have no experience with this dash, but the GM wiring schematics are showing the instruments are powered by the CLSTR fuse which is active only with key in Run position (not in Crank position), so I'm guessing parts of the dash stop working during engine crank.

 

Just an idea....

My car sat many years and as I was doing wiring continuity tests (before any power applied), I noticed the key switch was sometimes a bit finicky. I took apart the ignition switch and found the copper contacts had some light corrosion (dull in appearance) and continuity was intermittent depending where I probed the contacts. I used sand paper to clean up the terminals and it's been working perfect for almost 10 years now.

Also, the ignition switch actuator rod has to be adjusted properly to make sure the switch contacts are positioned well to make good electrical connections when key is moved between switch positions.

 

Back then, most of the Terminals and Contacts used in the Interior, were not Plated for corrosion resistance (as used for the Exterior of the Car).