So recently the fuel gauge began acting funny in my 72.It went from working, to working part time, to now not at all. The funny thing is, every now and again it will come on an read about 1/4 of a tank. And usually when it's about to run out, it reads it, that's how I know when to fuel up. Anyway, does that sound like a float or something electrical?

 

All the fuel sending units are the same from the 60's to the 200o's
Maybe search these forums plus the Electrical forum for NUMEROUS threads regarding gauges.


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It's most likely electrical. You need to conduct a resistance test on the gauge and that will tell you for sure.

 

[updated:LAST EDITED ON 15-Oct-02 AT 06:10 PM (EST)]I've had to repair the fuel gauge system on both my 1970 and my 1959 F100's.

I suggest the following:

1) If the fuel tank is still behind the seat, pull the wire off the sending unit and momentarily ground if (with ignition switch on). Watch your gauge; it should move at a fairly rapid rate toward the full mark. DO NOT hold the wire to ground very long; just long enough to note full movement of the gauge. If the gauge does not move, you have either a bad gauge or a wiring problem. If teh gauge does move, proceed to the next step.

2) Remove the sending unit from the tank (five or six screws) using a 1/4" socket or wrench. Be very careful not to tear the cork gasket or the rubber 0-rings/gaskets on each screw.

3) Connect a Volt-Ohmmeter (set to read resistance, 200 ohms or less) between the mounting flange and the stud for the gauge wire. With the sending unit held in a position similar to its mounting in the tank (the float is all the way down), the ohmmeter should read approximately 75 ohms (empty tank). Now move the float slowly to the uppermost position. As you do so, note that the ohmmeter moves somewhat linearily from 75 ohms (more or less to 0 ohms (full tank). If it doesn't, the sending unit is bad, and requires replacing. If it does, the resistor section of the unit is OK -- move to the next step.

4) Having proven the gauge and the resistor to be OK, the float is now suspect. Hold the unit close to your ear, shake it and listen for fuel sloshing around in the float (these brass floats get paper-thin over the years and may develop a slow leak). If there is fuel in the tank, you have two choices; repalce the float or repair it. If you chose to replace the float, a float from the 1976 - 78 Mustang II is identical.

If you decide to repair the float, use a resin type solder (being sure to get all the fuel out before applying heat). Try to keep the amount of solder used to a minimum, since it affects the weight of the float, hence the reading of the gauge.

Good luck
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