Pressure Regulating Valve - How to Test??

If you are talking about testing the proportioning valve, you would need 2 pressure gauges, And some fittings, it would be easier to test on the car, put one guage on the input side of the valve and one on the output side

When you press on the brake pedal, the input side should read higher than the output side. ( Like 1000 psi in = 100 psi out. Just numbers I pulled out of my but)


For brake warning light:

Off the car
You may be able to take a small rod and insert it into one side of the valve and manually press the piston to one side.
A multi meter measuring resistance will tell you the spool has moved and the switch is good.

Air pressure would work too.

On the car:
Open a front or rear bleeder and press the brake pedal. With the key in run you should see the bulb light up,

Blead the brakes as normal and assuming the warning light spool has centering springs it should go out. If it is still on open the rear bleeder and slowly press on the brake pedal till the light goes out and close the bleeder.

A multi meter measuring resistance will tell you the spool has moved and the switch is good.


That's my 2 cents and how I would approach it.