Initial investigation...
The unit I found had three wires and a rubber hose coming out of it.
I snipped the wires where they went into the main loom.
I followed the hose became a plastic pipe which eventually lead to the brake servo, on route it went through a "unit" which had 2 wires, again snipped where they went in to the loom.
The wires from the vacuum pump were red, brown and a thinner black one with a white tracer.
I tried several permutations to try and get the pump to work but nothing succeeded.
I tried researching on line but could only find info about the basic pump with 2 wires so I gave up and lost it in the shed.
Tidying up a couple of weeks ago I came across it again and decided I had nothing to lose so stripped it down.
The pump looked fine so I turned my attention to the electrics and this is what I found!