Composite Research, Inc.

Composite Research, Inc.
Makers of Sundance, Sea Born, and Spyder Boats

How do I test if my fuel gauge/sender is working correctly?

The following article is intended to assist owners and or marine service professionals in troubleshooting improper fuel level gauges that may be outside of the accepted 5-10% variance caused by EPA diurnal systems. When troubleshooting fuel gauge anomalies, we recommend starting with the fuel tank’s sender unit as this is most commonly the source of incorrect readings.

Step 1) Test the Sender’s Voltage:

  • The senders can work with both 12V and 24V system. The sender draws power through the gauge connection.


Step 2) Test if the sender is connected correctly:

  1. Check to see if the sending unit is receiving power from the gauge. The reading at the sending unit will be less than the input voltage at the gauge.
  2. Check the sending unit’s ground. The ground wire must be properly grounded to a common ground or to the negative on the battery.


Step 3) How to test if the sender is operating correctly:

  1. Disconnect the sender wires at the sending unit.
  2. Connect the 2 wires to an ohmmeter or multimeter and set signal to resistance.
  3. Take a measurement of the sender at empty and full positions. This can be done by either draining and then re-filling the tank which the sending unit is installed, or remove the sending unit from the tank and then manually operate the float by hand.
  4. For American Standard, the meter will show 240 ohms at empty and 30 ohms at full.


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