Fuel Gauge Sender Unit
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Senior User
Joined: Apr 2006
Posts: 201
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From: Hacienda Heights, CA
Fuel Gauge Sender Unit
My fuel indicator stopped working on my F-1, so I removed the old sender unit, tested it, and sure enough, it was broken Checked the circuit by touching the ground to the power wire, and the gas gauge came to life. So I ordered a new unit from Carpenter (said it was good for 6 or 12 volts), hooked it up before I installed it, and tested the circuit to see if everything worked. The gauge went to full when I moved the arm to the upper position, and empty when in the down position, but in the middle the gauge still reads full! Thought the unit was defective so I sent it back for a replacement, and the replacement unit does the same thing! My tank either reads 100% full or 100% empty but nothing in between. Is there something wrong with my wiring, or are these replacement sender units just junk??
Fleet Mechanic
Joined: Mar 2005
Posts: 1,462
Likes: 185
From: Dedham, MA
I bought one to put in and didn't like it. I went back to the original which got wonky below 1/2 and just put gas in when it gets there.
I had a similar issue with a 6 volt sender in an old Volvo, too...the replacements just don't work right with the original gauges.
I had a similar issue with a 6 volt sender in an old Volvo, too...the replacements just don't work right with the original gauges.
Parts Nerd Extraordinaire
Joined: Sep 2010
Posts: 4,358
Likes: 1,778
From: Western NY
As an FYI, The stock sending unit and gauges use the The King-Seeley (Ford Stock) principle. These sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train (that does have some adjustments available to the brave). Most after market sending units are simply a variable resistor which sends a constant voltage to the gauge, lessening that voltage as the fuel level goes down. Therefore, the sending units signal doesn't heat the bimetallic strip in the gauge as much. Unfortunately, the calibration of the after-market sending units and the stock gauges don't match up very well due to the differences in the principle of the signal.
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