It is a 4 pin molex connector on the fuelsaver,
with 3 wires coming out.
You should be able to check which is the
normally closed, common and normally open from looking for the
corresponding colour wires on the microswitch on the APS.
Using a multimeter (checking the lead resistance by touching them together),
look for less than an ohm resistance between the normally closed and
common on the molex connector.
Doing it this way will also check out
the wiring to the APs as well as the pressure switch itself
The aps body should have one or two rubber hoses connected to it.
Pull the other end of the tube off so you can activate the APS by sucking or
blowing. Depending on which tube, either suck or blow GENTLY to activate
the microswitch and test the common to normally open contacts on the
molex connector, again this should be less than an ohm.