No single ball -17 or -35 bally game checks the outhole for a ball before starting. Only the multiball games do.
(No single ball stern mpu100/mpu200 does, either)

Run the solenoid test through at least once to reset all the drops and get the ball out. Next press the coin door test button until you get into switch test (flashing 0 on the match display).

Press and hold the credit button you should get 06 flashing on the player displays. If you do, that tells you the credit button is being seen by the machine and your problem lies elsewhere. If you don't, or get a different #, that tells you there's a switch matrix issue.

Make sure none of the diodes on the switches on your coin door are shorting against something like the coin door itself. The slam switch in the coin door is notorious for causing issues when it's shorted. Also the ball roll tilt or the plumb bob tilt can have issues if shorted. Some of those switches have a capacitor that likes to short with age on them and they need to be replaced (for testing you can just clip one lead)

See pinwiki.com in the classic bally section for switch matrix issues if you haven't already gotten there.

Stuck lamps point to a short between lamps and switch wires. JUST chased this down on a mystic pf swap both the GI and the lamp feed had pierced the same column wire holding it high. The switch strobe would hold the lamps on, and the lamp activation enable for the 4514 on the lamp board would hold the switch strobe high all the time instead of pulsing.

You can test this theory by pulling the lamp fuses for both gi and controlled and see if your switch column wakes up.

Also measure for continuity between GI sockets and lamp braid and the switch column at a switch. There should be none.

You mean between the sockets/braid, and the switches. The sockets are connected through the braid and bulbs have continuity as well.

Dolemite pinzrfun described what I'm talking about perfectly. Put your meter in continuity one end on the switch column wire (at a switch is easiest) and then use the other probe and touch the sockets, etc. (power off).

Lamp sockets.

There should not be continuity from the braid or the lamp sockets to the switches.

yes if continuity figure out what's touching if not it's going to be something else but who really knows what at this point

my similar situation was especially confusing because I had crossed wires to sockets in 2 different circuits.

Like I said there should be no continuity between the lamps and switches you need to find the short.

You're not really following what you need to do. The short can be ANYWHERE the switch column and the lamp voltage is present so you need to check ALL lamps and wiring. It's been suggested to make it easier on yourself by disconnecting various connectors to narrow it down. I don't know what else I can tell you. You're reading continuity where it shouldn't be and you have to find it not just keep posting looking for a magic bullet.