Don't remember exactly without looking under the dash but mine had 2 connectors with about 20-30 wires each. I think the connector closests to the front of the boat had the grey wire which is the tach wire from the engine, towards the rear of the connector. Hopefully yours is similar and this helps you find it. The tach function is only used if you want to calibrate the PP for pulling skiers but if you are like me, you want everything to work like it's supposed to even if you don't use it.
You shouldn't have to run a wire from the motor to the perfect pass, unless that is what the instructions tell you to do. Just need the raw tach signal from the motor to the control unit, not the wire from the control unit to the tach.
Good luck, let me know if this helps-Brendan