Look in the manual, find the driver transistor for that pop bumper and test it. It’s probably bad and it’s always providing a path to ground.
https://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#Special_solenoid_problems

Resurrecting this thread. My sorcerer pop is locked on as well. It was 100 and all I did was go to adjust gap on switch cuz they were a bit sluggish. Anyways left pop is locked on. Transistor tests fine. I replaced cap resistor and diode on switch stack. Not sure where to go from here.

Drew the next thing I would try is unplugging the connector at the motherboard and testing at the board. That way you’ll know if it’s a playfield issue or a motherboard issue.

If I unplug special solenoid ground it still locks on. So I think its playfield but after changing out parts...still stumped

If by unplug the special solenoid ground you mean the input from the pf to the board, and it still locks on, it's the board. (Or at least where you would start).

Unplug both the input and output you can then measure the output connector pin that goes to that pop - if it has continuity to ground, the transistor, predriver, or logic chips are bad. You can test those with a logic probe to see which one has the errant signal that it shouldn't be. You can even get clever and ground the input pin and make sure the logic levels change.

Did you adjust the switch with the power on?

For others' future reference, the cap/resistor combo just provides a minimum length pulse so that the pop can react. One lead cut will not cause the circuit to lock on (but if it were connected and the cap was shorted, it would)

Thank you for that. I think I narrowed it down to shorted transistor and yes I stupidly adjusted switch with power on that caused the short.

-Drew