You can enable remote logging by making a circuit between pins 10&11.

Can't help with the exact part for a pressure switch - you would need a normally open pressure switch that operates at your desired minimum pressure.

When I had this - I used a relay triggered by the sprayer on/off electrical switching to close the circuit.

The thread below has some good info.

https://talk.newagtalk.com/forums/thread-view.asp?tid=398432&posts=8&highlight=Fm750%20coverage%20switch&highlightmode=1#M3171301