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Purpose of the Different Colored Wires on the Garmin GFS 10 Power/Fuel Gauge Lead

The GFS 10 is a fuel level / flow sensor that can be tied into a fuel system for measuring fuel consumption as well as fuel level in the gas tank. Installation of this sensor can be done via CANet or NMEA 2000 and has the option to connect to a fuel gauge.

Connecting to a fuel gauge or fuel tank allows the GFS 10 to obtain fuel level readings rather than just fuel consumption information.

The GFS 10 has two cables, one for interfacing to a chartplotter and one for the power / fuel gauge

There are four wires in the power / fuel gauge cable. A Red / White, Black / White, Grey and Brown

  • The Red/White wire is what supplies power to the GFS 10 sensor

  • The Black/White wire is the grounding circuit for the sensor

The Grey and Brown wires have different connection protocols based upon the boats fuel system. A fuel tank indicates its level by changing the resistance to ground on the brown wire. In order to read the fuel level, a GFS10 or fuel gauge must apply a current along the brown wire. Below are three different situations for wiring the GFS 10.

  • Fuel gauge is used, fuel tank level sensor is present: The fuel gauge is already providing current to the fuel tank along the brown wire, so the GFS 10 must not. The grey wire is connected so the GFS 10 knows not to supply current on the brown wire. The GFS 10 reads the fuel tank voltage on the brown wire, and compares it to the grey wire to determine the fuel level

  • Fuel gauge is not used, fuel tank level sensor is present: The GFS 10 must provide current to the fuel tank on the brown wire and measure the voltage. The grey wire is left unconnected so the GFS 10 knows that it needs to supply current to the fuel tank

  • Fuel gauge is not used, fuel tank level sensor not present: The grey wire is left unconnected on the GFS 10 and the brown wire is grounded so the GFS 10 is in a stable state (tank reads full for USA or empty for Europe)

For further information about the GFS 10 installation process, follow this link and click on installation instructions.