Frank,
On Gottliebs, when you see switches labeled something like P2G, P3A, P4E...those are switches that are on the player unit in the backbox. The player unit has switches in stacks that ride on the edges of several cams that all rotate together when the player unit gets a signal to fire. The switches open and close in a repeatable order as the player unit rotates. In that sense, it's much like the score motor, except that it's driven by a ratchet mechanism and solenoids, rather than an actual motor. Mechanisms that rotate that way are called steppers, as opposed to the score motor.
The "P" indicates it's on the Player Unit, the number indicates which cam the switch is riding on, with Cam 1 being closest to the steel ratchet. The last letter indicates the level of the particular switch in the stack, with A being the lowest level, and going progressively higher, or farther away from the cam edge.
You can jump a score motor switch (or any switch) by having a piece of wire with alligator clips on both ends, and clipping them on to the tabs on the back of the particular switch you're trying to bypass. If you can't get to the switch tabs (sometimes, there's very little space) you can follow the wire out from whichever side of the switch your interested in on the schematic and clip it somewhere else along the same piece of wire, since that piece of wire and the tab are electrically connected (theoretically, anyway). Jumpering is useful in "forcing" a switch or section of a circuit to be closed, to see if that changes behavior and helps you find where the problem lies.
PLAYER UNIT SWITCHES (resized).png