J Seery provided a great article discussing, "How Ford Gauges Work"
In this thread,
https://www.fordbarn.com/forum/showt...Work&showall=1
Also starting on page #96 of the Techno pdf linked in my signature below.
"When the ignition switch is on, current flows through the circuit and warms the Sending Unit bimetal by means of a heating coil, causing the bimetal strip to bend and open a set of contact points. When the points open, the current is interrupted allowing the bimetal to cool and close the contact points again. This cycle then repeats and the points vibrate open and closed pulsing the current in the circuit.
Because the current through the heating coil in the Sending Unit also flows through the heating coil in the Gauge Unit, the amount of heat supplied to the gauge unit is about the same as the heat in the Sending Unit. The amount of heat in both units is controlled by the average current flowing through the circuit due to the repeated opening and closing of the contact points."