misreading temp gauge

What, use the IVR? Who knows. Many claim it's because they already had 6V gauges. I don't think so. I think it was to attempt to get them more accurate. That is, battery voltage varies all the way from below 12V (lights on, idling, cold winter night, heater running at stop light) to 14V (charging down the road with battery "up) so that's a pretty fair variance. If this was your home power this would be about the same as a change from 100 to 120V AC, and THAT is a pretty large change!!!

So the IVR I think was intended to try and proved a bit better regulation. These were designed before "solid state" (transistors) really got off the ground

Ford by the way used essentially the exact same system. I can still well remember the day I climbed into my 60 Ferd Falcoon and the two gauges both went "through the roof."

Didn't take me long to figure that out, and this was long before Al invented the internet, LOL, this was fall of 67 before I joined the Navy.