Verify Wiring and Common Ground
Verify your wiring is good and that the gauge and sender both have a good common ground. We recommend grounding the gauge and sender together to eliminate any potential issues with not having a good common ground.

Verify Ohm Signal from Sending Unit
Disconnect the signal wire connection from the sending unit and verify the ohm output of the sender at various positions with an ohm meter (i.e. 0 ohm @ empty, 50 ohm @ half, 90 ohm @ full). Verify that you have the correct range fuel level gauge for your sending unit.

Verify Your Fuel Level Gauge Range Matches Your Sending Unit
Comp II LED fuel level gauges have a sticker on the back of the case indicating the range of the fuel level gauge (i.e. 90 for 0-90 ohm, 73 for 73-10, 240 for 240-33). You can verify the fuel level range setting for a SCX gauge by following the calibration procedure in the instructions and noting the location of the pointer after entering calibration mode.

Confirm the Gauge is OK by Using a Known Good Signal
Disconnect the signal wire connection from the gauge and use a 47 ohm, 100 ohm resistor and a 0 ohm (signal connection grounded) to verify the gauge operation with a known good signal. Install one end of the resistor to the gauge signal connecton and the other end to the gauge ground connection. For a 0 ohm signal input, ground the signal connection.

• For a 0-90 fuel level gauges: 47 ohms is approx 1/2 of a tank, 100 ohms is Full +, 0 ohms (signal grounded) is Empty.
• For a 73-10 fuel level gauges: 47 ohms is approx 3/8 tank, 100 ohms is Empty -, 0 ohms (signal grounded) is Full +.
• For a 240-33 fuel level gauges: 47 ohms is almost Full, 100 ohms is approx 3/8 of a tank, 0 ohms (signal grounded) is Full +.