Probably on the coin door interface board.

LTG

I wouldn't go replacing stuff unless you know it's bad.

And don't over think this, you have a basic switch matrix problem.

Switch wired wrong, diode reversed, or a short to switch wiring or switch lugs. And it can be anywhere in the game.

Give things a quick look see. Williams used a simple wire code for their switch matrix. Comparing switches helps you understand it. Just white wires and green wires. Different color stripes too but for basic checking just worry about the base color.

On a micro mini switch you have three lugs, two close together on one farther away. The two close together - the outside one gets the white wire and black end of diode, the middle one gets the green wire, and the far one gets the silver banded end of the diode.

Start digging, both sides of playfield and be sure nothing on top of coin door is hitting the front underside of playfield. Go over ramps too for pinched wires and stuff punded into switch lugs.

LTG

You have to remove at least one leg of the diode to get an accurate reading.

Diode has a silver band on one end, the other long black end goes to white wire.

LTG