A&P practice standards thankfully don't dictate the FAR's. There are many parts that are installed at the factory, the point of a minor alteration is that they can be replaced.

https://planelogix.com/img/blog/DemoPA46_POH.pdf is a POH for an early Malibu that requires a Hydraulic pressure gauge. it's a standalone gauge that just reads from a pressure line.

It also has a required equipment list. Included on that list are a taxi light, landing light, interior courtesy light, instrument panel dimmer switch and all manner of standard parts that could be reasonably replaced as a minor alteration. You don't have to use a General Electric part number 4596 for a landing light indefinitely nor do you have to keep the same hydraulic gauge part number.

I retract my previous opinion that this "could" be a minor alteration:

From FAR 43 Appendix A:

"(a) Major alterations—(1) Airframe major alterations. Alterations of the following parts and alterations of the following types, when not listed in the aircraft specifications issued by the FAA, are airframe major alterations:
.......
(ix) Hydraulic and electrical actuating system of components."

The gauge is part of the hydraulic system, therefore specifically spelled out by the FAR as a major alteration.

The gauge is not an actuating system. It's removal in no way affects the function or actuation of the system. By that logic you can't change the landing gear knob either.

Congrats on your new plane - early Malibus are just the ducks nuts.

whatever gauge you install will most likely need the markings carried over, green arc/red line/etc.

It is one of the simplest gauges I have ever seen in an airplane. Only one small red marking at 1700psi for high pressure, which I have never noticed till I looked at my picture. A John Deere hydraulic gauge would actually provide more information .

Here is a picture of the malibu gauge.

edit to show John Deere gauge below

yeah that screams owner produced part.

or this

https://www.aircraftspruce.com/pages/in ... essTSO.php

That one does look good. Nice and readable.

I have a good original hydro pres. gauge, along with a full set of gauges & indicators from early Malibu for sale. PM sent.

https://www.aircraftspruce.com/catalog/ ... _press.php

add your redline.. on the glass or have an instrument shop add it to the dial.

Thank you all for the thoughts and feedback. The Spruce gauge would be perfect, but it’s back ordered for 8 weeks. Thankfully I found a place to overhaul mine. So, I have a solution.

I would have no issue with a John Deer gauge. My other ride is a 1960 Twin Bonanza and you would be surprised how many of the parts are tractor / car / marine parts. I suspect a 2020 tractor part is far superior to a 1984 airplane part. The whole point of owner produced (often owner specified) parts is to keep planes flying when there is no other alternative. A situation where the original manufacturer has been out of business for decades and there is no other alternative certainly qualifies.