Thank you, Atari, for the link.
Very helpful.
It turned out that I had a combination of problems.
Once I hooked up the pump to the system again, I had a flashing 4wd light. This turned out to be a leak at the hose that links the pipe to the diff, and the last issue that I solved.
The pump pressure switch was turning off the pump at 5psi, when I had removed it and set up a guage to bench test it with. Same problem as discussed in the link.
The pressure switch is a very simple setup once you manage to take the assembly apart far enough to get to it. It is just a small diaphragm in a cylinder. As pressure builds the diaphragm expands and the rod that it's attached to pushes on a micro switch, when it overcomes the resistance of the return spring.
I stretched out the return spring to give a little more resistance and ended up getting 8 psi before the switch is activated.
The output signal on the pink wire was 10.2v and I wasn't getting a 4wd light. I spent a few hours scratching my head, thinking that the control unit would need 12v as a signal, before I found the leak at the diff.
Once I fixed the leak, with fishtank air hose, the system pressurised in two seconds and the 10.2v turned out to be enough of a signal to give me a light on the dash.
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