After too many hours crawling around under my Paj, and discovering that unused muscles dislike being called upon, my front locker is in, working and (briefly) christened!
After seeing the wiring diagram, I now understand what Grant was saying in the last thread, about the locker not activating if the compressor isn't switched on. But I wired the locker through the front diff switch anyway, using a relay.
The details, for those who are interested:
Power for the relay coil comes from the compressor relay coil, and the coil is earthed through the diff switch. The relay contacts are in series with the ARB solenoid, and I've put the relay in a socket, so if the circuit gives problems I can pull the relay and short out the contacts. Like Ado, my dash lights worked fine until I switched off the compressor, which I believe is because the two relay coils were providing a high resistance path to earth and confusing the ECU. A single diode in the line to the switch fixed the problem.
Found a patch of dirt beside the road not far away, and did some (low speed) circle work. The steering is noticeably heavier with the locker on, but not as heavy as I expected. The centreing of the steering wheel is scary.
From near full lock, idling in 4H 1st, when the wheel is released it really whips around. Anybody leaving their thumbs in the wrong place will soon learn! 
I found a short steep bank back onto the road, with a drainage ditch at the bottom. The front wheels hit the top just as the towbar dug in at the bottom, and that's where the car stopped. Hit the switch, the front wheels spun briefly then I was up and out.
Now I've gotta give it a real workout...
Cheers,
Scott
) and it's always on, so I don't have to think quite as much. And I have no idea where I'd put that switch anyway. 