fuel gauge not working (help)


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By lawdogg1 - 13 Years Ago
ok guys I need some technical help. I am trying to figure out why my stock fuel gauge for my 56 f100 (12 volt system)is not working (the needle wont even move). I replaced the fuel tank sending unit and float and replaced the gauge with another stock one that worked perfectly fine on another 56 f100. I then tried running a neg and pos wire from the battery straight to the fuel gauge and the needle moved all the way up to full (So now i know it is not the gauge). What could the problem be..im lost now. what should i do. Any help would be great.
By Rono - 13 Years Ago
Did you test the resistance of the sending unit with an ohmeter before you installed it? If you move the float up and down you should see the resistance change on the meter. If the sending unit is working and the guage isn't working, then you have a disconnect somewhere between the sending unit and the guage. Also, the fuel guage has to be matched to the sending unit. If you have an aftermarket guage hooked up to a stock Ford sending unit, chances are it won't be compatable.

Rono

By bergmanj - 13 Years Ago
Rono,

IF this guage system is the same as the sedans of that vintage (I personally do not know for sure); then, a simple resistance check with an ohmmeter will not, and should not, show any resistance differences when moving the sending-unit float.  It would be a King-Seely system, which does not use simple resistance changes to make the guage reading change.

To test the system properly, both the sending unit, and the guage must be in an actual powered circuit because the system uses a heated-wire wound around a bi-metal points contact system at both the guage and the sender.  the sender has a diaphragm which changes the spring tension on the bi-metal, changing the point at which the points open; that, in turn, changes the "heat" in the guage, thus changing the guage "hot-wire", which changes the position of the pointer.  The points opening and closing is what makes the guage "pulse" a bit (slowly).

This system was used on '54 & '55 as a 6-volt system, and in '56 as a 12-volt system: Parts from the two different voltage systems ARE NOT interchangeable; 6-V parts must be used with a 6-V system, and 12-V parts with 12-V only (some folks have used their old 6-v parts on a 12-v conversion; but, it usually "burns-out" fairly soon).

Regards,   JLB

By Rono - 13 Years Ago
JLB;

Thanks for correcting me. I apologize for posting mis-information. I was recently working on my boat sending unit which operates differently and since that fiasco was fresh in my mind I passed it on. I hope I didn't cause anyone any additional grief.

Rono

By lyonroad - 13 Years Ago
lawdogg1, I fought with the fuel gauge/sending unit in my 56 merc M100 on and off for a year and I believe that what bergmanj says is true for the pick ups. The truck shop manual says "If the indicator hand goes beyond the scale on the opposite side of the scale (I interpret this to mean reads past full) or reads erratically, a wire in the fuel gauge circuit is grounded or the tank unit is defective" The gauge can be checked by : Placing the ignition switch in the off position and connecting the terminals to two series connected (1.5v) flashlight cells. The 3 volts should cause the gauge to read approximately 1/2 full". Although suppliers of aftermarket sending units claim that their units will work with the stock gauges they will not. I tried 3 and the Mid Fifty catalog supports this assertion. I ran 5 volts to the stock gauge and it almost worked until the 5 volt voltage regulator failed. I ended up purchasing a new gauge with modern innerds made to look like a 56 gauge along with the compatible modern sending unit. I was converting to an after market rear mounted poly tank so the new sending unit fit the new tank. I am not sure if there is an adapter so that you can use a modern sending unit in a stock tank. Hopefully you can find a good stock sending unit if necessary. Good luck.
By JstinchcOmbE - 12 Years Ago
Hi, I know I'm late, I had the same problem with my gauge and after nearly giving up I tried putting good quality gaskets on the gauge terminals and just like magic, fixed.
By Hoosier Hurricane - 12 Years Ago
Lawdogg:

I'll try again, I posted a reply this morning and it isn't here. The fuel sender has to have a good ground to work. Just because it is mounted in a steel tank doesn't assure a good ground, sometimes the tanks lose their ground. Try hooking a jumper wire from the sender base to a known good ground and see if the gauge works.
By Doug T - 12 Years Ago
'56 gauges are different than all other Ford gauges in that they run off stright 12V but otherwise more similar to 6V earlier gauges. The senders in the tank and the head are different also.

When I had my '56 truck I converted it to '57 or later gauges which use the little voltage regulator gizmo to give about 7V average voltage. The wiring stayed the same but I used the much cheaper and more available later senders. The later gauges will fit in the earlier dash boards and for max authenticity you can reuse the behind dash '56 gauge housings. The later gauges will also fit at least '55's 'cause I did it to my T bird when I converted to 12V.

BTW Jim the site looks great with the new software