Air Pressure Gauge Not Working - Help!

[AMDenels]

Let's see if I can finally share pictures. This shows the mechanism above my door that uses air pressure to open the door. As I'm removing the ceiling panels and replacing the door I had to disconnect the wires to get the panels out. Since I move the bus to work on it the gauge still showed enough pressure for me to move it back and I thought everything was fine.

The next day when I went to move it the gauge wouldn't show the pressure rising. Fortunately it was a simple as reconnected the ground wire (the white one hanging down in the middle of the picture) to the ground (copper colored blob towards the upper right area.)

 

[Mark_In_MA]

I think that ground wire must have had something to do with the gauge itself. I couldn't release the parking break because the gauge was reading as too low. Once I reconnected the ground wire the gauge shot up showing the pressure was high.

i could see an electric interlock based on the physical position of the gauge needle as a way to determine if the bus will release the parking break or not. Its almost a double failsafe - the bus needs to have air AND a working gauge - even if the gauge doesn't work (but theres air), you can't ignore it and drive anyways.