Continue Shopping.
View cart with tax and discounts.

Fuel and Temperature Gauges Troubleshooting

1972-1986 Jeep CJ's

Fuel and temperature gauges, like all parts on older CJ's, will wear out over time. You may, however, be able to prolong the life of these gauges by understanding some simple troubleshooting techniques. The following information, the image at the bottom of this article and a decent volt/ohm meter should help you do just that.

Understanding the Gauges

The fuel and temperature gauges shown below are laid out in a simple left to right configuration. Both gauges have wiring terminals and a large jumper/regulator strap running between them. The fuel gauge terminals are labeled S, A and I. Fuel gauge S terminal has a pink wire and runs to the fuel sender. Fuel gauge A terminal is the 12V side of the jumper/regulator strap. Fuel gauge I terminal has a red wire and is the 12 V ignition hot wire. The temperature gauge terminals are labeled A and S. Temperature gauge A terminal is the 5V side of the jumper/regulator strap. Temperature gauge S terminal has a purple wire and runs from the temperature sender. The jumper/regulator strap runs from a voltage regulator inside the fuel gauge (terminal A) to the temperature gauge (terminal A). A voltage reading at terminal A of the temperature gauge should be approximately 5 volts. A 12V reading here means you have a bad regulator.

Resistance Readings

Fuel Gauge Terminals:

  • S to Ground 68-72 ohms
  • S to I 19-21 ohms
  • S to A 19-21 ohms
  • I to A Zero ohms
  • I to Ground 49-51 ohms
  • A to Ground 49-51 ohms

    • The fuel gauge can be tested by running a 100 ohm resistor from terminal S to ground (this will simulate the fuel sending unit). You should get the following readings: 73 ohms (empty tank), 23 ohms (1/2 tank), 10 ohms (full tank).

    Temperature Gauge Terminals:

  • S to A 19-21 ohms

    • The temperature gauge can be tested by running a 100 ohm resistor from terminal S to ground (this will simulate the temperature sending unit). You should get the following readings: 73 ohms (Cold-Test when engine is slightly warm. A stone cold engine will read 400 ohms), 9 ohms (Hot). A voltage test can also be run by checking between terminal A and ground. A reading of 0V means that the gauge is bad.

    Conclusion

    Replacing both the fuel and temperature gauges is the surest way to eliminate any doubt about whether or not they are working. Their low costs simply don't justify the time spent analyzing them.

    Article Source: Morris4x4Center
    Back of Speedometer
    Fuel & Temp Gauges