Evidently these brake switches are pretty unreliable. As suggested on the Stalker forum I hooked it directly into a master cylinder to verify it. Luckily I had a spare that checked out. I may reget where I have located the switch if they are going to fail this often.
Someone also clued me into how the “proportioning” valve actually works. Far from actually reducing the hydraulic pressure that reaches the slave cylinders it only throttles fluid. The will reduce the rate of change of pressure, but not the ultimate pressure. This makes it essentially useless for what I wanted and I may re-plumb the rear brake system again and take it out.
Just so I could say I have made some actual progress today I greased all of the chassis fittings.