1996 Accord LX 4 cyl.
I have an usual electrical problem that I have not been able to diagnose yet.
When driving, the radio will flash off momentarily from time to time. When it does, the speedo will drop to zero then back to normal again. One time, the car even died and had to be restarted. It almost always happens when moving and not parked. A couple times when I turned the ac blower on the flash happened, and other times it is when I let off the gas. No clear pattern it seems.

It has an aftermarket radio, but it has been in there for a couple years with no problems, and I installed it with the proper adapter harness (no hack job).

The car used to have an alarm, but I removed it.

I took out the ignition harness, removed the remaining wires from the alarm, repaired and re-soldered the connections to make sure it was working o.k.

I tried moving the key around in the ignition with it "on", but the dash lights stay steady (no flickering). The car turns over and starts quickly every time.

I had the alternator and battery load tested in the car, and they passed.

I have made sure battery connections are clean and tight.

Fuses are tight, and all wires I can see are wrapped up.
Still, the problem persists. Has anyone else seen this happen, and is it some part trying to fail?