Is your tilt trip relay tripped? It's in the middle of the trip bank on the back door.

If it is, what happens if latch it (with power off) and try again? Does it trip immediately?

If it is not, then your issue is likely in your 50V circuit, which of course runs through everything. My prime suspect is usually control unit cam switch 3A. A lot of current runs through that switch and it is normally pitted enough that the slightest disruption kills 50V through the majority of the game - especially the startup circuitry.

if the game wasn't modified for free play, add credits to the register and turn the game on to see if they come off.

if they don't, manually close the anti-cheat relay. If it doesn't stay powered by itself, your 50V has a problem. If it does, manually close the start relay and see if anything happens.

the tilt trip relay only disconnects 50V to most of the machine. The circuits needed to reset the game aren't affected by the tilt trip relay state.

if your game used to remove credits on power-on, whether that still works will narrow things down.

manually closing the start relay and seeing if the start relay holds itself powered until partway into the cycle will also tell ya something.

if you push down the start relay armature plate and it doesn't stay on the coil top, or credits used to get removed and now don't, then BCP suggestion of CU cam 3A switch is good. The only other switches in the start relay hold circuit are search index 17B (top switch on search index unit) and much less likely replay reset relay switch E.

if manually closing the start relay cycles the game, then your problem is making the start relay power from the coin switch ... could be plug connections. A test is to:
1] turn on machine
2] manually close the anti-cheat relay. It should stay powered by itself
3] add a few credits to replay register
4] push red button

if neither red button nor coin switch work, only thing left is the plug connections, a E.B. play relay switch and a replay reset relay switch E. See schem around E3.

before reading any below, the search wipers spin all the time when you turn on the game, right? If the search index unit is powering and stopping the wipers, that's a problem.

assuming the search wipers are fine, credits should get removed at a steady cadence.

the start relay releases and re-energizes itself? What should happen when there's no credits is:
- you manually close the start relay and it keeps itself powered
- when the start relay first closed, the timer cams index and mixer latch coils power and the game starts it's cycle
- when the timer cams rotate around 45 degrees (typically ... I don't have timing diagrams for big time yet), the start relay unpowers and stays unpowered
- cycle continues until timer cams rotate 180 and lock
- sometimes units continue to step up, but soon stop

once the start relay unpowers, nothing should be able to repower it is switch D on it is opening correctly. D is the top switch.

did you mean the replay reset relay is powering and unpowering while credits are being removed? That would cause irregular cadence. The start relay is the middle one in the 5 relay bank, the replay reset relay is on the bottom.

got a voltmeter or jumper wire?

jumper wire:
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with no credits on the game, connect one end to wire 30 on the transformer. Wire 30 is the one that attaches to a bottom lug then loops up to a top lug. Connect other end to the middle blade on the left switch on the replay register (wire 48-2). Flick coin switch and see if the game responds.

If it does:
- turn off the game reasonably quickly to avoid holding some solenoids powered too long.
- move jumper end from replay register switch to CU 3A switch with the black/yellow wire on it (other wire on 3A is green/black ... same wire that was on the replay register switch)
- try the coin switch. If it works, search index 17B isn't closed well. If it doesn't work, CU 3A switch isn't closed well

voltmeter:
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game on. Stick one probe on wire 70 on any handy 50V coil or the 50V fuse. Put other probe on wire 48-2 on the middle blade of left replay register switch. Got 50VAC? If yes, hold down the coin switch. Still have 50V?

if you didn't see 50V on wire 48-2 or the 50V dropped way down when holding down the coin switch, then CU 3A or search index 17B is making no/poor connection. Move probe from 48-2 to to black/yellow wire 83-3 on the CU 3A switch to see what the 50V is doing there.

Great that you got it going! Sometimes it just takes a clear mind and some time to solve a problem.

Thanks for reporting the resolution!

couple notes:

1] don't always believe the manual, but always believe the schematic. There's only been a couple schem errors found, but many manuals have issues.

2] the timer cams index unit position on the shelf is adjustable. More-or-less centered in the range works, but if you shove it too far forward the switch stack will be partway up a cam lobe and the switch state may be wrong.