Thanks Bally.
I think I have converged to the root of the issues now, and it is most likely that the wiring to the drop targets and coin door are causing the problems. These are on the same "wiring chain" if you like.
I''ll work through tracing the wires on the playfield and address any issues as I go and also verify J2 and J3 pinouts.
Here is a photo of the drop target wiring. The braided wire across the switches had been removed from the black DT, so I've replaced it with wire (see pic). There are also wires omitted from a couple of the switch lugs...
