Ok, so I grounded the connector to the block, turned the key on, and the brake light lit up. This confirms the circuit for the light is working, correct?

I then hooked the connector back up to the valve, turned the key on and got no light on the dash. If I understand you correctly, Norm, as long as the valve is in the center position, I have an open circuit, and the light should not be on, right? Only when the valve shifts one way or the other, it closes the circuit and throws the light, is that right?

So, if that's the case, then the valve should be in the center (or correct) position, yes?

Also, when the connector is plugged into the SW, when I hit the key, should I see the light come on and then go out, or does it not come on unless the valve shifts position to close the circuit?

All I'm trying to do at this point is verify the circuit is working correctly, with the intent of checking the actual operation of the valve soon...(baby steps, right),?

Thanks,
Dave

 

You verified the circuit is working and yes if the light does not come on with the key in the on position then 99% of the time the shuttle valve is centered. The lamp test basically does the same thing you just did by shorting the wire to ground, except its done with the ignition switch when the key is turned to start or in my 67 case, accy. Quit dwelling on this, as long as the brakes work and your not leaking fluid, its time to move on to a new project or simply enjoy the car.

 

Aye Aye Captain!

 

Dave - You're correct on all of your assessments. On my 71 CS the lamp doesn't illuminate when the vehicle is turned on. I know the circuit works because my Parking Brake SW does illuminate the bulb. My brakes work just fine. I wouldn't spend another second testing the Differential Brake SW - your brakes have been working just fine & no reason to suspect the Differential Brake SW is not working. You're spot-on regarding how it works. Tee time 8:00am for me.