Members with 4 wheel disc systems: Can you lock your wheels?

If you have a Valve like the first one shown in post 57, or a Combination valve like the Second one, that has been gutted
And
The switch is grounded to the brass case, (which would turn the dashlight on), then one side of the system is not working. If it is the front system that has been shut off, then yur gonna have OP's condition. If the rear brakes have been shut off; then, depending on their efficiency, you might never realize it.
The way to center the valve and fix this, is to press on the brake pedal, and; open one side, or the other, one side atta time, until the light goes out.
If the dashlite is not on, go check the switch for continuity from pin to case-ground, which would be a bad thing. Afterwords fix the switch circuit. That shuttle-valve has to be centered, in order for both front and rear brakes to function properly and independently.