Start with the switch test.
https://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Switch_problems

Page 17 of your manual shows switch numbers.

You have to start somewhere. Switches not working or solenoids not working.

Start ruling things out. Starting with switches is a good idea. YeOldPinPlayer is helping.

LTG : )

The switches are scanned by the mpu board. The software decides when to fire the solenoids. It's very possible that the entire column is out at the same time via a bad connection via a connector, board pins, or broken chained wire. BTW they are pop, jet, or thumper bumpers. Mushroom bumpers refer to a specific different type of bumper that's a lot smaller, as seem on the playfield of Fireball if you want to look at a pic of one on IPDB.

Go into solenoid test, make sure the pops and slings are firing there. Then go to the switch test with all the drops up and the ball out and press each of the switches. I doubt that any will activate, so time to start tracing where the wires are going.

You might want to consolidate your various issues into one post BTW sort of a one-stop-shop.

Are the flippers working? If no solenoids on the playfield are working it could be the under playfield fuse.

If they fire in solenoid test, that would indicate the coils are working properly, but the switches are not. Check the wiring of the switches under the playfield, they are usually daisy-chained together, so if one wire goes loose, multiple pop bumpers will stop working. If wiring is okay, check the diodes of the switches. You say the pops aren't working, but you said that 5 switches aren't working? Is everything in ST4 (column 5) of the switch matrix out?
pasted_image (resized).png
pasted_image (resized).png

Those 2 "bumpers" on the bottom your referring to I think are the slingshots. Do what we've suggested

All good, helps to get your terms straight so we don't get confused, but we all start somewhere. I would bet if you go into switch test, that the rollover target, single drop target and saucer switches aren't registering either. Definitely a problem in column 5 of the switch matrix

Just start by visually inspecting for broken wires, then you can check continuity between all the switches that are daisy-chained in that column. They should all have a yellow wire with red tracers connecting them together on the part of the switch that has the leg of the non-banded side of the diode.

as suggested in post #11, manually test the saucer, single drop target and rollover button.....are they registering/working?

if the above doesn't work out then you could try:

try removing and reconnecting J2 on the mpu board.

you could also try swapping MPU J2 pin 5 (strobe 4) for J2 pin 4 (strobe 3), so pin 4 into pin 5 position

you could also try swapping U10 and U11 on the mpu board and seeing if problem moves elsewhere?

That'll do it! That especially tends to happen around the pops because they get a lot of action, and when the coils fire it slightly shakes the playfield. The individual strands of wire break, creating a slowly weakening connection, until one day it comes loose. Just keep in mind these games are ~40 years old, so shit breaking down is gonna happen, as frustrating as it can be.

great news, nice easy fix

personally i'd remove the other yellow/red wire, cut off the crap bit so to start new, strip back the insulation enough, say 1/4 inch on both, twist them together, 'tin' them (apply a little solder to the now twisted wires) cut back the now tinned joined wires and then solder them to the switch tab.

They are properly called Thumper Bumpers and Slingshots. (Mushroom bumpers are completely different).
Sorry for this anal post, as a former Bally guy I must add my 2 cents.