How odd... Now correct me if im wrong as i havnt taken a golf pump off the bottle for years, but doesnt the pump flip polarity to the rear screen, there is only one pump, so you run it forwards to the front screen and backwards to supply the rear screen. So somewhere along the line, the boot vac pump is leaking current into the circuit between the rear washer switch, relay, fuseboard and the pump its self. I would expect using the rear washer switch would then activate the vac pump if thats the case? I probe it and see how many volts there is, if you get a good 12v on the rear washer switch, but less when it does it by its self, i would suspect there is a short in a wire somewhere.... Sometimes all it takes is bad ground point somwhere to send everything crazy.
