All your dash instruments are daisy-chained together on a single data line from the MMDC computer. The individual gauge knows what part of the data stream it's looking for, and reads only that part of the stream. That way the oil pressure doesn't show coolant temp or the tach, MPH. This also means that the gauges don't have to be connected up in any specific order.
We had a problem on the Bus with the air pressure gauge falling to zero periodically, then recovering. It also turned the low air warning horn on, so it definitely got my attention. Talking to Freightliner wasn't much help, because they said if it wasn't broken, they wouldn't be able to fix it. Of course I made sure all the gauge plugs were tight and such, but that didn't help. I dropped the instrument cluster part of the dash and scrambled all the gauge plugs.
Problem solved, never happened again.
Worth a try.
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