This sensor is really a simple switch. While it looks to have two wires (yea it does) they are strapped together at the male connector pins in the switch. ( see below). Look real hard down into the throat of said "proportioning valve switch" and you will see them connected together. One lead goes to the protective, smart, expensive, control box (yea that one) (pin "C" a box test circuit) and the other goes to the simple brake LED. When plugged into switch they are the same and are HALF of the circuit.
The little "plunger" protruding from the switch housing and into the valve is the "LINK" to making the switch contact. It DOES NOT close the two wire connecting to the switch. IT DOES provide a ground to the two wire (remember they are now connected when in switch) when in contact with metal shuttle and switch stated.
Here's the tricky part of this HUMMWV system. When the proportioning valve shuttle moves.
This metal shuttle valve when centered (normal) has the center area machined away to allow the pin to float in the normal state. Should a excessive pressure differential be detected the shuttle moves to the failed or low pressure side makings contact mechanical and electrical, grounding the pin and it is further pushed up to make contact to the other contact in the plastic switch. Remember those two wires are at the same potential... one goes to box the other to brake LED. This is where some get tripped up.
The problem and SERIOUSNESS of this is the valve detected a fail. Could be during a brake bleeding, low or no fluid in master cylinder, leaking system or in some cases slamming on the brakes in a panic stop. It is possible for the LED to flash or stay on and THAT needs to be address. If it stay on there is a little reset button to re-center the plunger on the end of the valve housing.
THE PROBLEM and now you know .... it is the same circuit as the emergency brake lever switch and this can / could send a person into a tailspin looking for a fix. To be sure, the emergency brake needs to be off / released. Still have a brake lamp lit... could be the the proportioning valve. If left disconnect... you will never know of a failed system.
Keep TM's handy and know your HumV, CAMO
More Sunday Funnies >
https://www.logsa.army.mil/psmag/archives/PS2009/678/678-12.pdf
This cut away may help. Some switches do make a contact between the two wires. Switch would have a plastic plunger (typical) BUT NOT HMMWV M998
View attachment 829159 Close to the Hmwv for view of contact plunger pin.
And the TM print of switch. See the two wires connected together when inserted into switch. This tells box it is plugged in. >
View attachment 829160 Was this helpful ???
