Key switch is located on the left side of the cabinet, in the front 1/3.

Alignment of each of these switches is critical.

It's kind of a relay - they were installed in the mid-60s starting around the time the 20 holers came into being. They are used for quickly adding credits back onto the machine.

Player hits big, but the bar owner doesn't have the cash to pay them. In that case, they could 'come back' (it's called the kumbackey) and present their IOU to get the credits back on the machine. Pretty neat idea, along with the separate cash box/diverter.

Unfortunately, the keys are almost always missing, and many of the games I work on have those switches out of alignment from multiple moves. One switch basically releases the replay cams index and another shuts off power to the rest of the game.

The cam itself provides pressure on the switches in the default position, and it needs to be tight.

I don't - I just make sure they are adjusted properly. But I like keeping things original where possible. You can always replace the lock itself if you wanted to, and didn't have the key.

Edit: yes, that's the kumbackey mech.

There should be a plastic 'ladder' that the switches fall into. The lock tab hits that. There should be pressure applied to the ladder during normal operation. The switches themselves should change state if the lock tab were to swivel. Make sure that they change state completely if the key is turned and removed in the lock position.

Yep! That keeps you from sticking in money when you have money already. Kind of a nice feature that many operators cut out - but there is a coil called the coin lockout behind the coin mech that will auto-return coins to you if there are credits on the meter.

We are here for you when you are ready to connect it back and troubleshoot.

Playing comes in phases -
1) Coin phase or betting phase - insert coin / play red button to start a new game. Balls dump to trough. First ball lifts to shooter lane.
Continue playing red button until you have the odds/features lit that you wish.
2) Playing phase - shoot the balls to try to get 3/4/5 in a single colored section. The 20 hole games have something called 'star zones'. These numbers don't count as part of the greater colored section until you have the other 4 lit in that section. They are used independently for the star zone scoring features. In order to assist the player, a feature called Mystic Lines exists on Tahiti. By pressing A/B/C (if lit and before the game locks you out of the feature [4th or 5th ball]), you can physically shift the bingo card numbers around on the backglass! Very neat. Tahiti also has a Ball Return feature. This will allow you to return one whole set of balls back to you to replay with no penalty, in case you didn't make the 'hit' that you wanted.
3) Scoring phase - finished shooting and nudging and panting trying to get that 5 in a section? Assuming you have 3 or more in a section (not counting star zones) or a set of star zones lit with the feature, you can press the R button to collect your winnings. These are applied to the replay register directly. Wait for the credits to rack and then you can press the red button to start a new game (see #1).

As Vic mentions in his excellent writeup, you have to get a feel for the machine. I find on the 20 holers that I can typically get a good hit in the green section.

Blue is also pretty good if I mess up the green.