replacing fuel gauge and sending unit on 55 ford wagon

[poolplayer1]

I bought a fuel gauge and sending unit that were on a 56 ford country sedan wagon. Both were tested there at the wrecking yard before I bought them and both checked good. Yesterday, I installed both and after I did,I get no reading at all from the fuel gauge. I do have 12 volts on the gauge. When I replaced the sender, to make sure I had good ground, I ran a seperate wire from the sender to the body. I have 12 volts at the sender wire. This is what I can't understand, If I remove the sender from the tank and than hook up its wire and put a good ground to its body, as I move the sender arm up and down, the gauge will rise and fall accordingly. So, I put the sender back in the tank, connect its wire and nothing again ,no reading at all from the gauge. Even though I had 12 volts at the sender wire, I still installed a wire (inside the wagon) from the sender to the gauge and it made no difference, no reading from the gauge. I think there is a bad or no ground at all somewhere but I thought I would ask the pro's here for their opinion on this problem. Let me know what you guys think about this problem. Thank you.

[miker98038]

Let me make sure I understand this. If you hang the sender in mid air (like a string from the trunk lid), hook up the wires, it works.

When you set or bolt it into the gas tank, it doesn’t. Same wires, same connections?

[poolplayer1]

Yes, that is what I am saying. I know it sounds weird but that is what is happening. I can't figure this one out. I am usually a pretty good troubleshooter but this time I can't figure it out. Both gauges are good. If something was loading down the power to the sender, I would not have 12 volts to it but the 12 volts are there at the sender. Can you answer this for me, what is the purpose of the sender unit having 2 spade connections to it rather than just one. There is only one wire coming from the gauge to the sender.
Thanks Miker98038.

[Abe Lugo]

I would double check wire schematic but I think there is a reducer on the back of the dash pod that reduces/regulates the voltage to 6 on the sender and the temp gauges. Just checking. I honestly don't think it's a direct 12 volts.

You can actually take a tester and check to ohms readings without having to worry about the gauge.

Last I would check the wiring behind the dash and the gauge to make sure that's all good.
Then follow the main wire back or check from one end to the other for continuity just to make sure it's not grounding out.

Basically check for faults in the system if you already knew the sender was working.

[wellcraft17]

The extra spade connector on the sending unit was for a condenser to reduce static on the radio. There was also a condenser on the coil and voltage regulator. Still have them on my56 f100.

[poolplayer1]

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Thanks guys for your help. There is continuity on the wire that goes from the gauge to the sender. Before I installed the sender in the tank, I checked the resistance of the sender when in empty and full position and it shows 10 ohms and 75 ohms or close to that.
According to the pro's here, the 56 model was the only one that came out with a 12 volt system. The wagon that I removed the parts from had the letter and # on its serial M6 and that would indicate that it had a 292 motor and is a 1956 model. The gauge has on its body stamped 12V. Since my wagon was originally a 6v, I don't think I would find a reducer any where in gauge line. My car is a 55.
I am going to see if I can track the problem this morning and hopefully fix it.

[dmsfrr]

Originally Posted by poolplayer1

.... I think there is a bad or no ground at all somewhere but I thought I would ask the pro's here for their opinion on this problem. Let me know what you guys think about this problem. Thank you.

Pretty sure you answered the question. The body of the fuel tank and the sensor are most likely not grounded to the body of the car, to be able to complete the circuit.

These fuel tanks are usually mounted into or onto the car with rubber blocks and strips in an attempt to eliminate metal to metal contact wear/damage from miles & miles of vibrations. (and subsequent fuel leaks)

If you have an Ohm meter or continuity checker there has to be a good electrical connection between the body of the fuel sensor and body of the car.

Run a new ground wire from one of the mounting screws on the fuel sensor to the body of the car.
.

[miker98038]

I agree with what dmsfrr says. But how I read it was you already had an auxiliary ground from the mounting ring to another body bolt. And in free air, it works. Then leaving all that in place, you put it in the tank and it doesn’t work. Have I got that right?

One thing to remember is that not all body bolts provide a good ground. In too many old cars there’s enough corrosion that what should be good isn’t. It might read with an ohmmeter, but won’t carry current (even small amounts) properly. This doesn’t sound like your case if it’s working in free air, but not in the tank.

How much fuel in the tank? As in what should it read with the float floating? No baffles in the way, total drop on the float no more than tank depth? Any chance it’s something mechanical rather than electrical?

[poolplayer1]

Found the problem. Well, it was nothing electrical causing the problem. After checking everything possible, I removed the sender from the tank and looked at the bottom of the float, it was dry, no hint of fuel on it. So, that meant to me that the float arm was not long enough to touch the fuel. I than checked with a ruler the depth of the tank and it measured 7.5 inches. Looking at the drop of the float arm, it would drop to 5 inches.
Just for the heck of it I went back to the wrecking yard where I bought the sender to measure the depth of the tank in the 56 ford country sedan and it measured 5 inches deep. I can't believe how much deeper the tank in my 55 is (7.5") and the other wagon being only 5 inches deep. Being that the arm float of the 56 was not long enough to reach, I could not get any reading at all. So, I started to bend the arm down and the first time that I did,I got a reading. I than kept on bending the arm down until I got to just under a 1/2 tank of fuel. Thats about how much fuel I have in the tank right now. I think I'm going drive it for a while until it gets close to empty and see how the gauge reads. I'll do some more adjustments if I need to Until I get it right. Since the gauge and the sender are from the same wagon (56) I think they will work good. Thanks to all of you that helped with idea's and suggestions on this problem.
Note: I had removed the sender from my wagon a long time ago (Had not been working at all) so therefore,I was not able to compare both to see the difference in the arm lenghts.

[miker98038]

Glad to know it’s solved. Nice that you posted the solution and maybe save someone else down the road.

[poolplayer1]

Yes, I'm glad the problem is solved. When I was there at the wrecking yard removing the sending unit, I than looked at the wiring under the dash and the parts that were still there on the wagon were 12 volt, including the bulbs and flasher. So, its true that the 56 model cars and wagons were all 12 volt systems. This is what most of you guys were saying. Now, on to working on the shocks.
Thanks miker98038 and all that helped. It is greatly appreciated.