The "Add Bonus" coil or the "Subtract Bonus" coil? Depending on which is 'firing', the debug path is different.

Also see if the Q relay is activate. That's the Bonus Score relay, and a switch there will cause the score motor to run. And also check the zero position switch on the Bonus Unit, to see that it opens when the Bonus Unit has reached zero (if it's subtracting).

These will be shown on the schematic, to find the logic paths involved.

I think what dirtflipper means by "path" is strategy, not electircal circuit. If it's the step down coil, the bonus unit zero switch is out of adjustment.

I do mean circuit. But the schematic shows the logic for the circuit, and not so much a literal wiring diagram, so I settled on "logic path" instead of circuit.

Still need to know whether the Bonus 'firing' is adding or subtracting, and then go from there.

that's the subtract coil. So if you manually actuate that so that the Bonus Unit steps back down to the zero position, check to make sure the zero position switch is opening.

I just fixed this problem on an Aztec. The leaf switch on the coin unit that opens at four players was on the wrong side of the post. It was bent down and closed at 1 player, then at 2 player the post rotated up and the switch opened...no more players. I got the leaf on top and adjusted it so the post opens the switch at four players. That solved that issue.