So I've installed an aftermarket stereo in my 88 GTU, and now the stereo power keeps flickering on/off.

First, I had only 3v at the Blue/red wire on factory harness so radio wouldn't even turn on.
So I ran a wire direct to battery to 12v constant on the aftermarket radio harness to test. Radio turned on when I turned the key.
Next I went over diagram and saw that 12v constant on car harness goes through 7.5amp fuse. I read somewhere here that is the ROOM fuse. So I tested at the fuse panel, and had 12v at room fuse. Then, with fuse out I tested blue/red and still had 3v.
I saw on fuse panel there is also a METER fuse at 7.5amp, so I pulled that fuse and still had 3v at blue/red.
So I put the fuses back in because obviously the factory harness is wired strange.
Suddenly I now had 12v at blue/red. Figured maybe loose connection and when I was fiddling around it sorted itself out. So I connected stereo harness to car harness and deleted direct battery test wire.
Now the stereo blinks on/off and I can hear a very faint clicking sound in the dash which is in time with stereo on/off. Like a very weak relay sound.
I don't think I'm connected to power antenna relay because before I looked at my FSM I was testing for 12v constant with a multimeter and tried connecting to blue/yellow and my antenna went up. This is how I discovered the antenna was ground switched.

Anyone have any ideas what might be going on?
I really don't wanna rip out a 35year old plastic dash, and would rather just run a new fused direct wire (but that doesn't solve my mystery, which will bug me until the end of time)

 

NM. Somewhere between here and there my head unit messed up. If I knew how to delete the thread I would

 

Turned out it was the factory ground (red/black) for the stereo. I switched to a ground from stereo lighting harness and everything works.