Since these are Williams games, it might only be 30V. You could tap off of any nearby 30/50V source if you wanted to. There probably isn't a lockout coil on the coin acceptor (Heath chute or coin slide?).
It was obviously connected at one time (with lamp cord) or the counter wouldn't be that high. From the factory, those counters had a few numbers on them as tests, but not thousands.
I would wait to test until you had access to the rest of the internals. Are the heads locked on the side trim or on the back door?