Quoted from Grinder901:
I removed my coin door and shooter rod housing, swapping them out and while the shooter rod is back, the coin door is still gone. I thought it would still play without a coin door but no luck.
That is likely the coin door interlock switch (The big fat stick like button that gets depressed when you shut the door).
If you pull it "out" it should be set up to act as if it were closed and allow you to play a game.
However it is there for a reason (so people, cats, etc. do not ge fried if the game is up and being worked on, or the coin door is open).
No joke, within 15 minutes of owning my first pinball game our new kitten jumped inside and I fired a game up without knowing he was in there.
That was almost 15 years ago now, and the cat is still going strong, but considering it was an Earthshaker to boot it must have been a bit of a ride for him