This assumes that you have some electrical knowledge and have sources for parts.

You will need:  
•  A space in your instrument cluster for another gauge (perhaps replacing an ammeter)
•  A standard Ford OE fuel, oil pressure or temperature gauge (other than the OE ammeter, which will NOT work as the core for this conversion) that has the same form factor needed to fit the space in your cluster (assumed nominal factory gauge resistance value of about 12.5Ω for this exercise)
•  Resistor or combination of resistors that will give you a total resistance of 85Ω to 90Ω, 3 Watts
•  A way to make and print a gauge face for your new voltage gauge.

A lot of people are replacing their factory ammeter with voltage gauges.  Most people send their gauge out to be converted, but if you have a spare "standard" gauge available, you can do your own conversion.

The premise is basically the same as is used in the temperature, oil pressure, and fuel level gauges.  The only difference is that the "sender" resistance value is constant and the voltage applied is varied.

If you're replacing your factory ammeter, you'll change the wiring to the replacement gauge by supplying 12V (e.g., from the 655 red wire for the '66 Mustang) to the new 85Ω resistor.  Then connect the other end of the resistor to one of the replacement gauge terminals.  Connect the other terminal of the replacement gauge to ground.


I did an experiment with a power supply and a spare gauge, just to get an idea of the gauge readings for different voltage inputs.  The positions of the gauge will vary slightly, depending on the value of the added resistor.  The gauge will read a bit lower for higher values of resistance, a bit higher for lower resistance values.  

Making the updated gauge face is an exercise left to the reader.  



 

Last edited by John Ha (6/03/2024 5:31 AM)