So, I've finally decided to take my games from not tilting to tilting and have run across an issue on my Pro Pool.
The previous owner had unsoldered the wires that run to the tilt mechanism switch. I reconnected the switch. Now when I try to tilt the machine, it only tilts momentarily. The tilt relay energizes and the tilt hold relay releases, but as soon as the tilt mech switch is released, the tilt and tilt hold relays return to their normal position and the game keeps playing.