Got started on the wiring harness last night, did a little more tonight. I have the common ground for all the microswitches in and the active wires in for the player one controls:
I took a couple more close-ups of the top side of the control deck. The player one controls, the spinner and the trackball, and the coin button!
With the player one all wired in I can now try the deck out. I am just tidying up the machine that will be running the emulator, getting the rubbish off it, and getting MAME and the controller configuration programs on.