Quoted from spinal:Makes sense since I see now I see they put one in all 3 directions: up-down, front-back & side to side under the playfield (pic below).
I'm new to the details of these machines so thanks for responding.
The under playfield one is a tilt switch, not an anticheat, same as the roll ball and the tilt bob (and meant to be the same wire colours too).
I think looking at the schematic gives some clues: 
pasted_image (resized).png
The bounce switch kills the whole 25v circuit. Obviously opening this was seen as very bad behaviour.
The coin door anti-cheat disconnects everything to do with the coin mechs and the hold relay. Preventing coin insertions faked.
The light box switch in Sky Jump is labelled as a tilt switch and only disconnects the hold relay.
Looking at Pioneer's schematic, the half moon credit unit has an additional anti-cheat switch which disconnects the replay button from the replay and start relays: pasted_image (resized).png
That makes me think the cheat they are protecting against is holding the button on the front of the cabinet while someone else hits the lightbox.
