Volt Meter Fluctuations 1988 M20J

[sailcail]

Hey Guys,

I’ve been having an issue with my volt meter for the last few months.  It intermittently fluctuates above and below the actual 28 volts.  I have a EDM 700 and the voltage remains steady at 28.1 volts and I have also tested it with a Fluke meter.  It’s definitely the instrument indicating incorrectly vs the actual buss voltage fluctuating.   My mechanic has cleaned the plug behind the instrument and the canon plugs in the wiring harness.  The wiring diagram shows five wires, one ground and two wires to the load and alternator shunts. In the video you can see how the voltage fluctuates above and below 28.

Any ideas?  Could it possibly be the instrument itself?

The plane is a 1988 M20J 205.

Thanks,

Simon

[Aerodon]

I have a replacement gauge out of a 1986 for you?  

[carusoam]

Looks Like all three needles are unhappy...

Typical of a single ground wire not working properly...

See if the ground wire fell off the panel... or if adding a simple temporary one improves things...

PP thoughts only, not an instrument tech...   see aerodon for better advice above...   

Best regards,

-a-

[Oldguy]

7 hours ago, carusoam said:

Looks Like all three needles are unhappy...

Typical of a single ground wire not working properly...

See if the ground wire fell off the panel... or if adding a simple temporary one improves things...

PP thoughts only, not an instrument tech...   see aerodon for better advice above...   

Best regards,

-a-

Anthony is saying what most of the problems end up being with similar symptoms shared here on MS. Could be a broken wire inside the insulating cover, something loose back behind the panel, etc. Probably one of the more costly and time consuming things to diagnosis and repair. 

[sailcail]

Thanks for the advise guys.  Does anyone have a pinout of the meter?  I've tried to get the model number off of the data plate but it's blocked by the air speed indicator.  We would like to add a temporary ground wire as suggested by Anthony and see if that solves the problem. 

Thanks,

Simon