Has anyone had any dealings with the 4WD system on these ?

There are basically vacuum controlled front wheel locking hubs controlled by a small control unit behind the dash.

The problem I am having is that the hubs after stripping and cleaning work ok with full vacuum applied to them but the control system seems to be playing up as follows:

Upon engaging 4WD the control unit switches on the solenoid to engage the hubs and signal is received by the control unit this has worked using a vacuum switch in the line to the axle, the hubs can be heard to thump but before you have chance to move the car to assist in engaging the gears it drops out again by switching off the solenoid. It however does not engage the release solenoid which it uses when you disengage 4WD.

The 4WD warning light stays on permanently not flashing during all this, My question is - should this flash or stay on (does staying on indicate a fault )?

Attached is the wiring diagram I have for the system and below is an explanation of what I have found on each wire:

Pin 1 Disengage solenoid - Works OK

Pin 2 Engage solenoid - Works ok

Pin 3 Warning light - Works ok (also NO ABS on my car)

Pin 4 Connection to ECM (Connected but no sure what it needs to see unless just engine running ??)

Pin 5 Earth - OK

Pin 6 Vacuum switch in line with hose to engage - Works OK when engage solenoid engages and a gauge shows a good 20"mg in hose

Pin 7 - 4WD switch in transfer box - Works OK

Pin 8 Dual pressure switch (Only on petrol engines) _ absolutely no idea what this is ??????? (Maybe Air con ??)

Pin 9 Connection to instrument (NOt sure what it reads fro this??)

Pin 10 Positive feed - OK

I hope to find another car shortly to test and work out what should be happening but if anyone familiar with this system could guide me I would be appreciated.

Cannot seem to upload the jpeg wiring diagram but could email to anyone interested !!