Pulsating Voltage in Gauge Wires??

The idea of the original late 50's technology for the gauge regulator/ limiter is "duty cycle." It produces an on/ off pulse that is "something close" to 50% on and 50% off. This then divides the power about in half. The reason the gauges don't "show this" is because they are very heavily damped---they move slowly. The original IVR worked similar to a turn signal flasher---a heating coil wrapped around a bi-metal strip heats it up and it moves, breaking a contact, and then cools off and remakes contact

These were used by Ford, Mopar, and I guess AMC. I don't know about anybody else. I don't think GM ever used a similar system

First encounter I had was in about 1967, I had a '60 Ford Falcoon for awhile. One day the gauges both pegged. I think the Motor's Manual belonging to my Father held the answer LOL