I have some old notes when I checked my 1969 rally gauges with the 5 volt linear (7805 type regulator):
Oil Pressure:
0 PSI, 74-82 mA, around 51 to 43 Ohms.
15 PSI, 108 mA, 30 Ohms.
20 PSI, 113 mA, 28 Ohms (2, 56 Ohm resistors in parallel.)
40 PSI, 136 mA, 20 Ohms
60 PSI, 156 mA, 16 Ohms
80 PSI, 172 mA, 9.79 Ohms (10 Ohm in parallel with a 470 Ohm resistor.)
Fuel Gauge:
Empty, 51 Ohms
1/4 Tank, 50 mA, 33 Ohm
1/2 Tank, 100 mA, 20 Ohm
3/4 Tank, 125 mA, 15 Ohm
Full, 150 mA, 10 Ohm
Temp Gauge:
120 Degrees, 62.1 mA, 62 Ohms
150 Degrees, 98.8 mA, 33 Ohms
170 Degrees, 119.7 mA, 22 Ohms
180 Degrees, 130 mA, 20 Ohms
225-230 Degrees, 160 mA, 13 Ohms
240 Degrees, 163 mA, 12 Ohms