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1970 Mark Inoperable Fuel Gauge

Hi Bill,

I have a 1970 Mark III with an inoperable fuel gauge. The needle always sits on empty no mater what quantity of fuel is in the tank. What do I need to do to diagnose and fix this problem?




Hello Patrick -

If the Temperature and Oil Pressure gauges are working, the best and easiest place to start is at the Fuel Tank gauge electrical plug.

With the key on probe the three female pins on the plug with a grounded test light. One pin will have continuous power, one will be flashing and one will have no power. Have someone watch the Instrument Panel Fuel Gauge as you momentarily ground the flashing pin to the car body. The gauge needle should rise quickly to full. DO NOT leave this pin grounded - if you do, you run the chance of burning out the gauge.

If the gauge does not rise or you do not have flashing power at one of the female pins, you will need to repair the fuel gauge circuit or the gauge itself as per the shop manual.

If the gauge at the dash does rise then you need to repair the Sending Unit in the tank or its ground wire (which is the female pin at the above plug) that has no power with the key on.

Most problems are in the tank Sending Unit or its float. Lincoln Land does offer repair service for these and the other components in this circuit. Good Luck and let us know how the repair goes.