Can alternator diodes "leak" and discharge the battery?

[Dale_K]

I've ordered the new VR and sure hope it fixes the car. Yesterday with the AC on the accessory voltmeter I bought occassionally showed less than 12v at idle.

About the gauges - I don't know about Porsche specifically but most modern cars don't operate the gauges from directly connected sensors. The gauges are controlled by the ECU, which decides what position to point the needle based on the sensor reading but the ECU is programmed to avoid alarming the driver with mildly high readings (temp) or low readings (oil & volts). The ECU puts the needles in pleasantly reassuring positions unless the underlying system gets really bad.

[JFP in PA]

One point worth considering is that the dash displays in these cars are notoriously inaccurate to begin with. The coolant temp typically displays near 180F, while the DME says the actual temp is more like 210F; this same display is also non-linear in accuracy (it is further off at some temperatures than others).

[Dale_K]

I haven't received the voltage regulator yet but I did perform a parasitic battery drain test today. The car had been sitting for many hours and I was careful not to open a door or do anything to "wake it up". I saw about 17-22 milliamps when I disconnected the battery cable and hooked the battery post to one side of the meter and the cable end to the other side of the meter. So I'm assuming I can rule out parasitic losses.

[JFP in PA]

That is correct; normal draw can be as high as 40-60, so if anything you are on the low side.