740 L4-2.3L SOHC VIN 88 B230F (1985)
The positive supply for both the fuel gauge and engine temperature gauge comes from the voltage stabilizer and is regulated at 10 volts + 0.2V
^ If both gauges show too much or nothing at all, the voltage stabilizer is probably defective. (check the fuse).
^ If one gauge is not operating the fault most "likely" is the sensor or wire leading to the gauge.
^ To test the gauge, install a 68ohm resistor (P/N 9995824-1) between ground and the white-gray wire (fuel) or white-yellow (coolant).
A correctly operating gauge should deflect 75% (tolerance + width of pointer).
If the gauge reads correctly, the problem is the sensor.
^ Incorrect gauge reading: