on the l8 4x4 the switch side of the magnetic clutch relay is feed from fuse 18,this relay is earthed by the dash switch when aircon is selected.the mag clutch relay now supplies main power to the idle speed compensation relay which when energised by a switched live (ignition i think) now supplies power to the compressor magnetic clutch via two system pressure cut off switches and drives the compressor via the v-belt
i would look at the dash selector switch first disconnect it and see what happens
if the activation earthing wire from the magnetic clutch relay is shorted to ground anywhere between the relay and the dash switch it would be the same as the dashswitch been selected on all the time and asumeing all else is wired correctly and its the same as the 4x4 then it could be your problem.
having it working is a good start as usually the problen is trying to get it to work
i couldnt get mine (4x4) to activate after a full engine/car strip down and rebuild,it turned out to be the throttle position sensor adjustment it was causing my idle speed to be at 2000rpm and this confused the ecu with regards to the idle speed compensation relay.
so lets hear how you get on