is 1090-106 the top number on the plate below the handle or the bottom?  The bottom is a serial number, and the top is a model number.

if you are a schematic kinda person, you can find paperwork in https://bingo.cdyn.com/slots/

all the versions of a model are pretty similar, so if in doubt look at the base 1090 schematic if a dollar machine or 1090-1 if quarters.

you need the coin unit step-up coil to fire, and thanks to bally's confusing nomenclature, that means you need the following to happen:

1] coin switch down for first coin, coin relay trips
2] coin switch up for first coin, handle release relay trips
3] coin switch down for second coin, coin relay powers and keeps itself powered
4] coin switch up for second coin, the coin unit step-up coil fires ... which releases the coin relay, which in turn unpowers the coin unit step-up coil and the wipers rotate on the unit.
5] repeat steps [3,4] for 3rd coin

so ...
coin unit = stepper unit with wipers
coin unit step up coil = solenoid coil on the coin unit with the plunger that sucks in when coil powered
coin unit relay = relay with switches and armature plate that pulls down onto the coil top when coil powered, changing the switch state.

often the problem is the coin relay is not keeping itself powered because the "step-up arm" switch on the coin unit isn't closed.  Look for the switch on the lever arm operated by the larger step-up solenoid with the yellow and blue/orange wires on it.  Make sure switch is closed unless the plunger is in the coil (you can test by manually pushing in the plunger and watching the switch).

this video may help to make sure the relay coils/solenoids work:
https://bingo.cdyn.com/slots/videos/50V_Jumper_Testing.mp4

All of them are lit except for the bottom one 24 volt

Check these LEDs on the Backplane board

I'm at a loss

I have gone through every wire checking its location, sometimes twice, just to make sure that both the: wire to plug orientation, and the wiring is 100% correct. I must have put 16 hours just into this issue.

Where is the best place to check the voltage.  I don't seem to be getting anything at the bulb.