YourEconProf

TL;DR: I can't keep my MS3x on for more than 30 seconds to 2 minutes at a time. Any suggestions on external pins to trace to try to narrow down whether problem is internal or external to the MS?

Okay...I have a 1990 NA6, has been running well on an MS3x built by Ohio ECU Solutions for 3-4 months, was on MS2 for ~2 years prior. Driving down the highway on Wednesday, straight up dies. Current situation/observations:
1) Replaced Main Relay & Fuel Pump relay, disassembled & cleaned ignition switch, cleaned both driver side grounds underhood.
2) If the car hasn't run for a bit, (30 minutes) and I turn key on, fuel pump primes, MS3 comes online, engine starts & runs for 30s-2m then just dies.
3) After engine death, if I try to restart immediately, no fuel pump priming, and MS3 stays offline, and engine cranks but won't catch. WBO and digital voltmeter in the dash both behave normally.
-> However, if I jump the F/P-GND then when I turn key to acc, the fuel pump primes and the MS3 comes immediately online.
4) When the engine dies, the MS3x goes immediately offline (from the laptop connected) and the lights on the MS3x all go out.

So I think that the MS3x is shutting down, whether losing power or because of an internal fault. I'm trying to chase it down (though I'm open to other suggestions). What pins should I check for power? What pins cause the MS3x to boot? Any other ideas?