On Pioneer, a combination of Player Unit switches and CX (2nd Player relay) control the advancement of the PU. Once the trough switch is crossed, P is energized and motor 2C will allow the second (of five) motor 1A pulse through to increment the PU once (to Player 2). Then, based on CX (in this case, a one player game) and switches on the PU itself (P1C and P2A M/B), 3 more motor 1A pulses will pass through (to Player 3, Player4 and then Player 1 Ball N+1). The first of these three (P2->P3) is enabled by the lower leg of the circuit and the other two pulses (P3->P4->P1) are enabled by the upper leg. In two player mode, CX is open and the lower leg is disabled.

Pioneer PU (resized).jpg