The diagram shows you the switch stacks mounted above each of the cams on the Player Unit. Player Unit switches in the schematic are labeled as:
Pxy where:
P: Player Unit
x: cam number
y: position of the switch in the stack, starting with A closest to the cam.

So when you see a switch labeled P2C in the schematic for example, it would be the 3rd switch mounted above the 2nd cam of the Player Unit. There is no correlation between cams and players that I'm aware of.

This is essentially the way score motor switches are labeled too. See for example https://pinside.com/pinball/forum/topic/sky-kings-power-free-play-and-top-hole-issue#post-4457680

/Mark

Hi mrbanjo
See here https://pinside.com/pinball/forum/topic/player-unit-gottlieb-4-player-game-royal-flush#post-4842927 greetings Rolf

The 5th cam has one lobe with switches that stops the unit at player 1, ball one during the startup sequence.

That can be thought of as the "home position" of the player unit, which also happens to be the state of the game captured in the schematic. In other words, just like they show the motor at its home position, bonus units at zero, etc., the schematic has that one lobe on the 5th cam pushing its stack up. (Because player 1 is playing, the 1st cam is also pushing its stack up.

On a four-player game, P1 is player 1, etc., up to P4 controlling player 4. On a two-player game (like Big Shot compared to Hot Shot), the 3rd and 4th cams are different, but there are still 5 cams and 5 switch stacks.
.................David Marston