1. Check the Sending Unit (most likely culprit):
* Location: The sending unit is located inside the fuel tank. Accessing it requires dropping the fuel tank (a messy and potentially dangerous job, requiring proper safety precautions including disconnecting the battery and letting the fuel tank vent).
* Inspection: Once you have access:
* Look for obvious damage: Check the float arm for cracks or bends. Make sure the float itself is free to move and isn't stuck or filled with debris. Inspect the resistor wire for breaks or corrosion.
* Check the connection: Examine the electrical connector for corrosion, loose wires, or broken pins. Clean the connector contacts with contact cleaner.
* Test the resistance: With a multimeter, test the resistance of the sending unit across the terminals as you manually move the float through its range. Your Chevy's repair manual will specify the resistance values at various fuel levels. If the resistance doesn't change as you move the float, the sending unit is likely faulty.
2. Check the Wiring:
* Visual inspection: Inspect the wiring harness from the sending unit to the gauge for any broken wires, chafing, or corrosion. Pay close attention to areas where the wiring may be rubbing against metal parts of the truck.
* Continuity test: Use a multimeter to check for continuity between the sending unit connector and the gauge connector. A break in the circuit will prevent a reading.
3. Check the Gauge Itself (least likely):
* While less probable, a faulty gauge is possible. This is harder to diagnose without a known good sending unit. If you've ruled out problems with the sending unit and wiring, you might consider having the gauge tested by an automotive electrician. Replacing the gauge is often a relatively inexpensive option if this is the problem.
4. Grounds:
* Poor grounds can affect the electrical signal. Check the grounds for the fuel gauge and the fuel tank itself. Clean any corroded ground connections.
Important Considerations:
* Safety: Working with fuel is dangerous. Always disconnect the battery's negative terminal before working on the fuel system. Work in a well-ventilated area away from open flames.
* Fuel Tank Removal: Dropping the fuel tank is a significant undertaking. You might want to consult a repair manual specific to your 1983 Chevy truck model for detailed instructions and diagrams. It often involves disconnecting fuel lines, brake lines, and possibly other components depending on your truck's configuration.
* Repair Manual: A factory service manual for your specific year, make, and model of Chevy truck is invaluable for this type of repair. It will have wiring diagrams and specifications for the fuel level sending unit.
In short: The most likely fix is replacing the fuel level sending unit. However, a thorough check of the wiring and grounds is necessary to rule out other potential causes. If you're not comfortable working on your fuel system, take it to a qualified mechanic. This is a job best done by someone familiar with automotive repair.
