# Fuel gauge and sending unit 801



## Travman (Jul 6, 2018)

Replaced gauge and sending unit on my 801(841) powermaster. Ran wire to battery, ran a ground, and ran wire to sending unit all from gauge. I got nothing gauge stays on empty. I can take off wire to sending unit and gauge goes to full. I only have about a 1/2 tank. I need help as I am new to this all. Thank you.


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## sixbales (May 18, 2011)

Howdy Travman, welcome to the tractor forum.

You should have two terminals on the gauge. The sending unit is grounded at the tank, so the gauge gets its ground through the sending unit. You don't need a ground wire. Hook the battery to one terminal of the gauge and the sending unit to the other. The terminal for the battery should have a mark on it (like B or + for battery).

Some gauges have 3 terminals marked as follows: B for battery, T for tank/sending unit, and a ground symbol. If this is your case, then you do need a ground wire attached to the ground symbol.

You can't leave the gauge permanently connected to the battery or the sending unit will run the battery down. Power should come from the keyswitch.


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## Travman (Jul 6, 2018)

sixbales said:


> Howdy Travman, welcome to the tractor forum.
> 
> You should have two terminals on the gauge. The sending unit is grounded at the tank, so the gauge gets its ground through the sending unit. You don't need a ground wire. Hook the battery to one terminal of the gauge and the sending unit to the other. The terminal for the battery should have a mark on it (like B or + for battery).
> 
> ...


There are actually 3 terminals B(+), T(-), and a ground. Then there is a light terminal too, but I'm not using it. I had the wires ran to the switch until I saw that something wasn't right. That is when I was just using battery terminals to troubleshoot . I am still not sure what is going on. I feel the parts should be correct, as I have bought many parts from this local place. Thank you for your help.


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## sixbales (May 18, 2011)

Your sending unit base is grounded to/through the fuel tank. You may not be able to get a good ground through the tank. Clean this connection to see if you can get it to work. Otherwise, run a ground wire to the mounting base of the sending unit.

To check the gauge, ground the T terminal, the gauge should read full scale. If you have an ohmmeter, measure the sending unit wire to ground. Move the float up and down and the resistance should vary. If not, then your sending unit is suspect.


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## Travman (Jul 6, 2018)

I did check the ohms with the sending unit ground outside the tank. The resistance did change.


sixbales said:


> Your sending unit base is grounded to/through the fuel tank. You may not be able to get a good ground through the tank. Clean this connection to see if you can get it to work. Otherwise, run a ground wire to the mounting base of the sending unit.
> 
> To check the gauge, ground the T terminal, the gauge should read full scale. If you have an ohmmeter, measure the sending unit wire to ground. Move the float up and down and the resistance should vary. If not, then your sending unit is suspect.


I did check the ohms yesterday and the resistance did change up and down with movement. When I have everything hooked up the gauge reads empty. As soon as I take the wire off the sender/tank and the wire not touching anything the gauge moves all the way to full, but when I touch it to ground or back to the sender the gauge goes back to empty?


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## sixbales (May 18, 2011)

Check your ground on the sending unit base. With sixty years of corrosion, your tank may not have a ground?


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## RC Wells (Dec 26, 2008)

You do not by chance have a 12 volt gauge on a six volt system, or vice versa?

The sender is the same with both voltages.


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## Travman (Jul 6, 2018)

sixbales said:


> Check your ground on the sending unit base. With sixty years of corrosion, your tank may not have a ground?


Sorry for late response I had to work. I did think of that, and ran a wire from ground post on battery to sending unit and locking ring. Still the same outcome. Gonna contact supplier tomorrow to see if they know what's going on. Hopefully just a bad gauge or sender or maybe the two aren't compatible. Thanks for the help


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## Travman (Jul 6, 2018)

RC Wells said:


> You do not by chance have a 12 volt gauge on a six volt system, or vice versa?
> 
> The sender is the same with both voltages.


Sorry for late response I had to work. The gauge says 6 volt on the back and the box. My tractor is still 6 volt. There are 2 more terminals on this new gauge than the old one. 1 for the light which I'm not using, and a ground. I have tried everything. Gonna contact supplier tomorrow to see if they know what's going on with it. Hopefully bad gauge or sender. Maybe the 2 are not compatible. Idk. Thanks for the help though.


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## RC Wells (Dec 26, 2008)

Your 6 Volt system was originally positive ground. Unless you purchased an exact replacement Ford fuel gauge, you likely got a negative ground generic version that uses a diode instead of a field shunt. Bench test the gauge and sender in a positive ground and in a negative ground configuration. NOT WITH THE SENDER IN THE TANK.

By bench testing, I mean connect the sender to the gauge outside the tank so the gauge is wired to the ignition and then to the sender with two wires, and then cycle the float arm and see if the gauge responds.


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## Travman (Jul 6, 2018)

The tractor is still positive ground. I can get the gauge and sender to work outside of the fuel tank, but I have to run a positive wire to the battery and another positive to the sender in addition to the sending unit wire, and a ground from the gauge. The gauge will move up and down like it is suppose to. If I leave the extra positive wire on the sender when I install it as soon as I touch the positive to the + post on the battery it just sparks, and doesn't work. I dont really understand the whole positive ground thing. I know there is something that I am doing wrong and can't figure it out. Sorry I know this all probably sounds real confusing to you. Thank you for your help.


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## RC Wells (Dec 26, 2008)

It sounds highly probable that you have the wrong replacement gauge for the polarity of the tractor. But I am guessing based on your explanation. If you have a gasoline 801 do not do any further fuel gauge jumper testing near the fuel tank, that is a recipe for disaster.

The original Ford gauges relied on a magnetic field coil on a shunt, and would work either positive or negative ground, so never were a problem with either polarity. Replacement automotive type gauges use a solid state approach that is polarity specific, and only work in an installation that is compatible with the designed polarity. Verify you have the correct gauge.

If the tractor were mine, I would be absolutely certain the tank is grounded common to the frame/engine of the tractor. Ford did this through a combination of the tank saddle and the steel fuel line to the gasoline carburetor, or to the filters/lift pump on a diesel. Take a volt meter and connect one leg to the negative battery terminal, and the other to the steel tank away from any open fuel cap or open fuel line. If you read the battery voltage at that point the tank is properly grounded. That assumes the battery polarity is positive ground.

If you do not get battery voltage, first verify the battery really is positive ground. If it is, you will need to remove the tank and clean the contact points outside of the saddle webbing. These are usually the clamp bolts at the side of the saddle straps, there will be metal to metal contact there. Also be sure the bolts that hold the saddle to the tractor are not rusted and losing contact. Unless you have a sender as described in my last paragraph here.

The way a positive ground fuel gauge functions is the key switch provides negative polarity 6 volts power to the gauge, then the wire from the fuel sender connects to the positive terminal on both the sender and the gauge. The gauge has two terminals, one for the negative 6 VDC from the key, and a second for the positive 6 VDC from the sender. The original sending unit has only one terminal, and that is the positive connection to the gauge, the positive ground is obtained through the sending unit mounting flange. 

Some aftermarket senders have a second wire terminal on the flange specifically for a ground wire, just connect that terminal to any braided copper wire with the appropriate connector that is in turn connected to a clean bolt on the block or the frame.


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## Travman (Jul 6, 2018)

That is alot of help. Thank you very much. I will try all that when I get home this weekend to work on it. Thanks again


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