Mystery oil pressure indicator switch

[Flyler]

Hello detectives.

I have a new, beautiful M20J. It includes a mysterious, unlabeled switch. My pieces of evidence:

1) when toggling switch, only noticeable change is that the factory Mooney oil pressure gauge pegs high. Toggle switch back, it goes back to normal reading.

2) chasing wires of switch, it appears to be a 2 position switch that interfaced with the oil pressure gauge. The wires on the other end of the switch head towards RH side of panel but are disconnected and tied off.

I would like to remove this switch one day, but am curious about what it may have done? Plane has a JPI700 and Fuel Scan 450.  Any idea what instrument may have, presumably, ingested oil pressure data when the pilot flicked the switch?

 

 

[toto]

Wild guess is that it’s a remote mode selector for the engine monitor. But this doesn’t even look like an aircraft switch, and there’s no mounting screws in it - so it might be something like an input selector for your audio panel. 

No clue about the oil pressure fluctuation. If you hadn’t chased the wires, I would guess the oil pressure gauge is affected by interference from whatever that switch is controlling. Having a mysterious unlabeled switch that directly affects your factory oil pressure gauge is undesirable. 

 

[Flyler]

Thank you for your input. I'm sorry if my first post was not clear- the switch is wired directly to the oil pressure gauge. It is a toggle switch. So in one position the oil pressure gauge works as normal and the factory intended. In the other position. The signal is sent off to a wire is not connected to anything. Perhaps it was at one point, but no longer. It is intentional as the connector is covered with shrink tube and zip tied.

[PT20J]

Is there a logbook entry?

[Flyler]

I'll look through logs now, but its coming out anyways.  Fortunately whoever put it in, did not modify any of the factory wiring and left the connectors there.  Since the other end of the switch wiring is disconnected/capped off, its easy to remove and not worry about.  Seems a lot safer than having that switch in the loop!

[skykrawler]

Did you buy the airplane from a person with no name or phone number?

 

[PT20J]

On 10/4/2025 at 4:24 PM, Flyler said:

I'll look through logs now, but its coming out anyways.  Fortunately whoever put it in, did not modify any of the factory wiring and left the connectors there.  Since the other end of the switch wiring is disconnected/capped off, its easy to remove and not worry about.  Seems a lot safer than having that switch in the loop!

Good idea to remove it. It’s questionable to modify the wiring for the factory gauge if it is still the primary indication.