Brake pressure warning switch

[uptboi31]

I have a few questions about the light. Is it supposed to come on when you turn the key on before you actually start the truck like the oil light comes on? If it is, my switch is bad, and if I have to change it, will I have to bleed the brakes after replacing it? I have not been able to find a switch at the common auto parts stores, only LMC seems to have it. If anyone knows that a regular auto parts store has it, let me know.

[Mancar1]

I have a few questions about the light. Is it supposed to come on when you turn the key on before you actually start the truck like the oil light comes on? If it is, my switch is bad, and if I have to change it, will I have to bleed the brakes after replacing it? I have not been able to find a switch at the common auto parts stores, only LMC seems to have it. If anyone knows that a regular auto parts store has it, let me know.

Does it go off once truck is running?

[uptboi31]

its not doing anything....not lighting up at all ever

[Mancar1]

Mine would come on with key on then go out when truck is started. Anytime I open the brake system I bleed my brakes.

[uptboi31]

Ok, I guess the switch is not working and i will have to get a new one then....I should add that I don't have power brakes if that makes a difference

[Hawkrod]

The switch on the brake distribution block only works when 1/2 of the system fails and you can't check the switch by turning the key. Also note that the switch is isolated from the brake fluid so you do not need to bleed the brakes if you remove it. If you remove it and it is wet with brake fluid you will need to rebuild the block because the seals have failed. You will actually know this before you take it apart because you will be using brake fluid. Hawkrod

[Hawkrod]

The switch on the brake distribution block only works when 1/2 of the system fails and you can't check the switch by turning the key. Also note that the switch is isolated from the brake fluid so you do not need to bleed the brakes if you remove it. If you remove it and it is wet with brake fluid you will need to rebuild the block because the seals have failed. You will actually know this before you take it apart because you will be using brake fluid. Hawkrod

[ultraranger]

Before I changed out parts that may not need changing, I would first ohm out the bulb to verify it isn't burned out or possibly a broken filament.

You can also take the connector pigtail loose, at the valve switch, and ohm out the switch (while the switch is still installed in the valve body) to determine if the pressure differential valve spool is centered (like it should be) or if it has shifted off center.

There will be two pins sticking up inside the plastic switch. Set your multi-meter for ohms and touch one lead to one of the two switch pins (doesn't matter which pin, they are redundant (bridged together). Touch the other meter lead to the outside of the valve body or, to any good chassis ground.

If the meter reads infinite resistance (open) then the spool is centered as it should be. If the meter reads 'zero,' then the pressure differential valve spool has shifted off center inside the valve body and closed the switch contacts which would illuminate the warning light on the dash --if the bulb is good.

You could also do this test using a multi - meter with the dial turned to Diode check. This setting will give an audible signal if the switch is tripped. If it's not tripped, there'll be no beep.

[uptboi31]

Ok, I'll check it with a meter, thanks ultraranger

[Madman]

It should only come on when there is an imbalance of pressure which causes movement in the switch. If you bleed off the pressure on the front or rear, such as when you remove the backing, the switch moves and closes a contact which lights up the light....it only comes on when you have that difference in pressure, indicating either the front or back brakes have failed...it should not come on when you first turn on the key....hope that helps!