Sounds like it might be stuck in tilt mode.
Check tilt relay or any of 4 or 5 tilt switches thruout the game.

Could be that the light on the Backglass for the tilt is burnt out?

Hopefully the labels on the playboard inside the cabinet
are in place, so you can identify the tilt relay,
and see if it is engaged with the game is turned on and a game is started by pushing the start button.

Check these tilt mechs first.
Especially look to see if the pinball on the incline tilt mech is stuck (uphill)

pasted_image (resized).png

Also please note that not all tilt relays (Contacts) are normally closed,
some might be normally closed. (Slam tilts might be an example)

If you can rule out the tilt being the problem,
then likely culprit based on your symptoms
is in the start up relays.

or maybe the hold relay

might try these videos

Actually that last video was not that helpful, for your particular problem.

Might try this site to see if it helps
http://www.pinrepair.com/em/index3.htm

Try cleaning first.
Or activate start relay and/or hold (or lock) relay by hand
Be careful not to shock yourself with game power on.

Does the game go into the game over mode or is it in the game over mode, prior to the start up mode?

What color or trace marking do those particular wires in question have?
Looks to me like black with white traces, but hard to tell and wire cloth insulation may be faded or dirty.
You will need a schematic for the game to help see where those wires might go
or are intended to connect to.
Also note:
That those wires may have been taped off on purpose and not intended to be soldered to anywhere..

You may be correct about coin mech.
This era WMS used a special coin mech that accepted nickels, dimes and quarters all in one mech. Very hard to find.
Good news is if that small jones plug is for the coin mech, it should not affect the game from playing, if you have other means to add credits.

have you tried getting a schematic from The Pinball Resource?