So I have this Gorgar I picked up last year thinking I could bring it back pretty quick. Now every single board has been rebuilt or replaced, the play field is totally polished and clean, every bulb had been replaced, new rubber, power cable replaced, and everything has been taken apart and cleaned then put back together. I want to thank Tim Nabours for all the board work. He's been wonderful. But now all the hard stuff is done.... It boots up, sound card works, lights all light, coins add, displays are all functioning, and the flippers work. The ball out hole coil isn't punching (no big deal, I'll get to that) but as things warm up and the machine vibrates or jostles, the displays go black and sometimes stay off. Sometimes they come back on but the game is reset without the credit and the total credits have decreased. I've had enough floating grounds and shorts in my automotive career to know a bad connection when I see it. All connectors are reseated and I've done the old "Ford Wiggle" test and had nothing from it. I can't find any indication of where to start pinning out wires. Anyone else with some functional knowledge could help send me in the direction of where to start with a wiring diagram and an ohm meter. Could the displays themselves cause a system reboot if they lose power? Any advice would be helpful.

I can double check but I know that the guy doing the boards was pretty savvy about conditioning those suckers. I'll check.

So after checking the chip sets on the MPU and the driver, I noticed that while I couldn't find a bad wire from wiggling, I did notice that anytime I touched the MPU and most of the time I touched the driver, it reset like I described. I suspected the pass through connector so I reseated the connection and all the screws holding down the board. That got the game started finally and a ball cycled out the outhole. Scored a few points, made some noises, and after the sling shots fired, it reset again. I'm going to check for a cracked solder joint or something next. Or some built up solder shorting out against the back. Such a weird issue.

Thanks a bunch for the suggestions folks. So, the 40 pin passthrough connectors male and female were both replaced. I'm thinking one of those might have had a cold solder. I'll check and maybe reflow them. That's a great place to start, thank you. I'll also thoroughly inspect and repin the power cable. That is definitely original and untouched so it might be listing voltage. The flippers are slow/weak anyhow.

Update: I started by putting both boards out and inspecting for cold soldering on the 40 pin. Nothing there. I reinstalled and it fired up, booted and even played through a single round. Then, when the ball drains it just sits on the outhole plunger switch. I adjusted and filed the switch and nothing happened. I played a few rounds by manually shifting the ball to the shooter lane everything worked at it should except the right flipper was a little weak. Then on the third round, the right flipper locked on. I tried to move it and it's got full solenoid power to it. I turned things off. Turned them back on and after it boots, the flipper goes right back on. I'm going to look up the wiring schematics to find the SCR to replace tomorrow after I clean and adjust the flipper mechanism. After all these random issues, after having both boards rebuilt, I'm not sure if I'm on the right track here or not. The switch not triggering the out hole plunger seems like a board issue to me. And the game still won't fully boot with the coin door closed. The diagnostic button results in two quick LED flashes and then off. So that's okay I guess.
Thanks again for the help so far.

Thanks Travish, I did not know you shouldn't file them. Oops. Luckily I have a few spare switches. I've paid much more for a lesson.

Solved! I had overlapping issues that were confusing me. Dead switches, dead outhole, displays shutting down, stuck flipper, boot failures, a whole mess. Through help here, other postings, and Tim Nabours, I was able to isolate each issue. The boot issues turned out to be a cold soldered pin on the MPU. The dead switches were a busted wire a few switches up. The flipper was a broken switch that the contact had fallen out of. Each time I pressed the switch out would fuse to the hot leg and energize the flipper. The outhole was a grounded power wire. At this point it's just waiting on a new flipper switch from pinball life and we'll be in business. Thanks for all the help. I love this message board community. Everyone is so helpful.