Check switch 38. White/blue wire and green/black wire.

GorgarSM (resized).png

A photo might be helpful. You mentioned via PM the other bumpers have multiple white wires and the top bumper only has one.

Checking to see if it’s stuck closed. It’s the switch that tells the pop bumper to activate.

Look at the switch. It will look something like this one.

I feel like we might not be on the same page with the repair help. Can you remove the glass? Raise the playfield? Use a multi-meter?

PopBumperSwitch (resized).png

Left Jet Bumper is switch 37. Does your switch test show switch 37 is closed?
https://www.pinwiki.com/wiki/index.php/Williams_System_3_-_7#Testing_the_Switch_Matrix

Not likely. Go into switch test and see if the switch is working there before you dig into further board work.