Also, I do not believe my valve is a proportioning valve, but rather it is a distribution block with a switch to light a dashboard warning light if either the front or rear brakes lose pressure. The valve has separate inlet and outlet ports and chambers for front and rear brake circuits, respectively, and a pressure switch between them that senses when pressure is lost in either circuit, illuminating a red warning light on the dashboard.
If anyone knows where I can find a direct replacement for my switch, please let me know.