TBM's wiring diagram of the instrument voltage regulator reminds me of the need for same. Late 60's and into 70's and beyond, fuel and temperature gauges worked on the bi-metallic principle where an electrical current would heat such a strip of metal which would distort in a manner proportional to the voltage driving the current, so allowing mechanical linkage of strip to gauge pointer. It also gave very damped readings which was an advantage with fuel sloshing around tank. The technology only worked with a constant reference voltage though, which battery charge systems didn't allow, hence need for 10 volt regulator.

It can be seen if regulation fails an erroneous gauge reading will ensue.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone