[John Mackie]

The dash gauges used on 1940/50 Fords consist of a bi-metal strip wound with insulated resistance wire. When the gauge is working the current passing through the winding heats the bi-metal strip which bends and causes the pointer to move across the scale. The deflection is proportional to the current passing through the winding. The sender (fuel tank unit or oil pressure sender) also has a bi-metal strip and a winding BUT one end of this winding goes to ground via a set of points, the other goes to the terminal which goes to the dash unit. As the temperature or oil pressure alters the fixed end of the bi-metal strip is moved by a diapfragm meaning that more heat is required to open the points. This requires more current through both bi-metal strips and also an altered reading on the gauge. The temperature gauge usually reads “backwards” with no current or the ignition turned off the needle points to hot. The later fords also had a temperature switch in the second head which opened if that head got too hot causing the gauge to read hot.

Enter the 1960’s. Cars had gone to 12 volt. The falcon still used c6 volt gauges fed with 6 volts from a bi-metal voltage regulator incorporated into the temperature gauge . this regulator supplied short pulses of 12 volts . which averaged out at 6 v. later cars used an “instrument cluster constant voltage regulator” Ford base # 10804. Mac’s list 4 types . all do the same basic job. All these work on the make and break principle and are responsible for the tick tick that can often be heard in the car radio. Solid state devices are now available that do the same job and cost a lot less