Still no reason why LED b20, guards closed, doesn't light. I took the control box apart and found a mess of TTL, this thing doesn't have a microprocessor. The control box has an input labelled b20 which lights the LED and does nothing else.

There must be another circuit board to nobble b20 somewhere in the cabinet which is an absolute rats nest of wiring. However, I now know which pin on the monster plug control box plug goes to b20. Armed with that I should be able to find this mystery board and see which of it's inputs is failing to light b20 and enable the hydraulics.

When I plug/inplug the shorting link on the optional core retract guard socket I can hear a relay click, so I am probably looking for a board with relays on it.

I shall keep posting, I know you lot can't help but somehow it makes me feel less alone