Fuel and Temperature Gauge Problems
Short answer: When the fuel gauge reads always-full and the temp gauge always-cold but oil and alternator work, it’s usually not a cluster ground — the Rally cluster’s grounds only serve the lights and indicators; the gauge circuits ground at their sending units. Since the oil gauge works, you have +12 V to all the gauges (shared feed on pin 10, pink wires), so each dead gauge has one of four faults: a broken wire to the sender, a bad sender, a bad sender ground, or a bad gauge.
Test the fuel gauge: Find where the rear harness meets the main harness (a 7-wire connector); the tan wire is the fuel-gauge circuit. On the connector coming from the front of the car, jumper the tan wire to a good ground and turn the key on (don’t start) for 5–10 seconds. If the gauge drops to EMPTY, the gauge and wire are good and the fault is at the tank (broken sender ground — most common — or a bad sender). If it doesn’t drop, the gauge or the tan wire to it is bad.
Test the temp gauge: The sender is on the intake manifold near the thermostat housing; its wire is dark green. Disconnect it, jumper that wire to a clean engine ground, key on. The gauge should jump to HOT — if it does, the sender is bad; if it doesn’t, the dark-green wire or the gauge is bad.
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Content last modified: June 13, 2026 at 10:06 am
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This has been helpful, but while I am now more informed I am still a rookie. My fuel gauge isn’t working either. I will test the from the rear connection forward as describe. But if I need to drop the tank and check there, what exactly do I test and how? Thanks.