1. Visual Inspection:
* Fuel Sender Unit: This is the most common culprit. You'll need to access the fuel tank (usually involves dropping the tank – a messy job). Inspect the sender unit for corrosion, damage to the float arm, or debris obstructing its movement. A faulty float can give inaccurate readings.
* Wiring: Carefully examine the wiring from the sender unit to the gauge. Look for broken wires, loose connections, corrosion, or chafing against the chassis. Pay close attention to the connections at both ends.
* Gauge: Inspect the gauge itself for any obvious damage or cracks.
2. Simple Tests (without removing the tank):
* Check the Fuel: The most obvious—is the tank actually empty? Sometimes the gauge is just inaccurate, not completely broken.
* Ground Connection: A poor ground connection is a frequent problem in older cars. Trace the ground wire from the sender unit and ensure it's clean and securely attached to a good ground point on the chassis.
* Tap Test (Gauge): Gently tap on the gauge itself while observing the needle. If it moves erratically, it could indicate a faulty gauge movement. This is a very crude test, however.
* Voltage Test (with multimeter): With the ignition on, check the voltage at the gauge's connection point. You should have battery voltage (around 12V). If not, there's a wiring problem. You'll also need to check for voltage at the sender unit connector—with the key on, you should read a voltage that varies depending on the fuel level (usually, the lower the fuel, the lower the voltage).
3. More Advanced Tests (requires a multimeter and some electrical knowledge):
* Testing the Sender Unit (Requires Tank Removal): With the sender unit out of the tank, you can measure its resistance with a multimeter as you move the float arm. Your owner's manual or a wiring diagram should show you the resistance values for different fuel levels. A shop manual is very helpful here. The resistance will vary depending on your car's specifics.
* Voltage Drop Test: You can use a multimeter to measure the voltage drop across different sections of the wiring to pinpoint any significant resistance issues. This would involve measuring the voltage at various points in the circuit.
Important Considerations:
* Safety: Working with fuel tanks is dangerous. Always disconnect the battery's negative terminal before working on the fuel system. Ensure good ventilation to avoid potential explosions from fuel fumes.
* Shop Manual: A shop manual specific to your 1960 Chevy Impala is invaluable. It will provide wiring diagrams, resistance values, and other crucial information.
* Professional Help: If you're not comfortable working with car electrical systems or fuel tanks, it's best to take your Impala to a qualified mechanic specializing in classic cars. They have the experience and tools to diagnose and repair the problem safely and efficiently.
In short, diagnosing a fuel gauge issue requires a systematic approach and some basic electrical knowledge. Start with the simple visual checks and then progress to more involved testing only if necessary and only if you're comfortable with the task. Safety should be your top priority.
