So my machines were nearly complete accept for some lights. So I changed out bulbs, that didn't work, I traced wires, checked voltage, nope nothing wrong. Finally I noticed that they were wired wrong, apparently from the factory (3 in a row). So I switched the wires around and viola! The next light had me totally baffled, until I realised it needed a diode which was also not installed at the factory. A fifth one had a broken diode. This was on a Data East game, my Williams is definitely better built and assembled.
So anyway, I had usually assumed the factory layout was correct but you really can't rely on that.
Family members called just to make sure I had the pins up and running and that they couldn't wait to play. They are certainly an investment I don't regret making.