I was curious about just what was the difference between the 6v and 12v gauges so I went out and did a little measuring just now.

Since the fuel sending unit is simply a resistor that varies between 0 and 30 ohms on Chevy's we'll assume that the sender is at the 0 ohm end and then we can figure the power (heat) generated in the gauge itself.

'38 truck fuel gauge - 30 ohms between the supply terminal and sender terminal

'64 Chevelle fuel gauge - 47 ohms between the supply terminal and sender terminal

Using Ohms law Power (watts) = (Voltage * Voltage)/resistance (ohms)

'38 gauge at 7 volts = ( 7 * 7)/30 = 1.63 Watts
'38 gauge at 14 volts = (14 * 14)/30 = 6.5 Watts
'64 gauge at 14 volts = (14 * 14)/47 = 4.17 Watts

That's the numbers. I ran my '49 without a dropping resistor and plan on doing my '38 the same.

'38 Chevy 1-1/2 ton
'49 Chevy 1/2 ton
'54 Chevy 6400 2 ton
'55.2 GMC 3/4 ton
'56 GMC 1-ton

No Room Left in Shop