N231BN

I understand that but don't over think the situation. He was in a constant descent and his airspeed went away. If he was in shear it would have taken a large pitch change to maintain 500 fpm. Pitch+power=airspeed. Also, shear associated with heavy rain is very turbulent. I think this is a case of an old dirty pitot system getting flushed in the rain.

Sarcasm right???

Make sure the panel mounts aren't sagging, if you have 1980 shock mounts they will not be in good shape. The ball might be centered but you aren't coordinated.

That makes sense I guess, thanks.

The OP doesn't have a FD, many C41 equipped Mooney's were sold with a plain attitude indicator. I would guess the computer is still set up for a DC though, not sure. FWIW, I much prefer a double cue flight director. They are more precise, especially in pitch. The Cessna 525 we had could switch between the two styles when you were flying. It may have been a better system than the King, I have never flown one of them. Our old 340 had a DC with the Cessna autopilot(century gyro I think), it was as precise as a glass display.

Find a way to measure voltage with the pump connected, I bet it doesn't stay at 12v. Your regulator is either bad or like mentioned above, you have a dirty connection somewhere.

At the end of the CSB is the warranty section. States 2 hours labor and parts included, am I reading that correctly?

The filter is there in case of a pump failure. The cowling is pressurized and can push air(and dust) through the pump and into the instrument after the vanes break. The situation you describe is impossible. Draw out a complete vacuum system on a napkin and think it over some more.

My 231 does the same thing when I turn on the pitot heat. I can understand the ground issue with the lights being grounded to the same panel that the gauges are but how could the pitot heat affect this? Perhaps a voltage drop in the CB panel?

The G5 will not provide attitude info to a Century autopilot. The G5 HSI can provide heading bug and course pointer signals. You will need to retain your attitude indicator or upgrade to an Aspen or Garmin 500 and add their converters to remove the original attitude indicator.

Has anyone tried to get a field approval since the STC is unavailable?

That is really cool that you are making those fairings. I wish those efforts could be spent making a lower gear door that eliminates the need for the fairing. One of the old Mooney mod companies had an STC for one but they are now defunct. However, that would require a PMA which any sane person would avoid like the plague. One of the main reasons those fairings get so beat up is when your shock discs become less pliable they don't extend the gear to the same length so the doors don't line up very well. A bad design on Mooney's part which was greatly improved on the 252. I'm in for a pair, thanks.

I think you misunderstood me, I just wanted the OP to know he needs to retain his vacuum gyro or get the above mentioned equipment to replace it.

Since it hasn't been specifically mentioned, the G5 will not provide attitude inputs for the century autopilot. You will need either a G500 or Aspen with their associated DAC's.

Make sure the battery is charged? Do you have your Approved Flight Manual Supplement?