I´m a bit puzzled by the use of so much wiring, when modern technique is available, and yes you can have modern teqnique and yet easily replacable and manageable machines.
Why not mill four groves into the bottom of the playfield, two for low voltage (+ -) and two for higher voltage needs.
Spray the groves with plastic liner for safety and zero risk of leakage.
Maybe it´s even plausable to have just two groves (i dont know the possible wattage-outtake from bumpers etc during for example a multiball)
Use digital switches or resistor-line technique for all sensory input.
Use digital leds for lighting.
Use same control-wire (as the leds) from led-controller to controll high energy items, such as bumpers, toys etc.
Where energy is needed get it from the groves.
This means you will have a total of two wires, and connectors locally to the groves and that´s it.
All serviceable by a layman.
If you then standardize ingoing, outgoing controller and the computer, you´ll have overview, serviceability and sustainabilty.
Sorry for any wonky expressions and errononous wording. English is not my forte.