Gas gauge problems
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More Turbo
Joined: Sep 2011
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Gas gauge problems
I rewired my 1955 ford f100 with a 21 circuit ez wire harness. The fuel gauge has a runts reducer. But the gauge won’t go past 1/8 tank. Ez wire said on the sender one wire goes from the tank to the gauge. And the other tab ex wire said just gets grounded. I did all this. So I put in another four gallons to see if the gauge would move. No luck. Any suggestions? I was thinking of taking off the runt reducer to test my gauge.
thanks
jerry
thanks
jerry
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
Where are you grounding the sender? Don't use one of the screws holding the sender because some trucks have rubber insulators under the tank. I had to run a wire to the cab to get a proper ground on my 49. 
Senior User
Joined: Apr 2019
Posts: 142
Likes: 4
From: Portland, CT
I also rewired with the 21 circuit EZ Wiring kit. My gas gauge was not registering correctly. So on Saturday, I removed the sending unit (which is new) to play around with it. While moving the float thru the full range of motion, I saw that the gauge was correctly registering the float movement. Then I placed the sending unit in a bucket of water to see how the float reacts. My observation was that the float shaft rotates, as the float shaft fits loose in the sending unit pivot area. IMO, this is a flaw, as the way the float orients itself won't allow the shaft to reach the "full" position. I then used a piece of safety wire to lock the float shaft in one position, and this did the trick. I had about 1/4 tank at the time. I then filled up, and my gas gauge correctly reflected those amounts. Sorry I do not have any pics to reflect what I've been talking about.
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I’m grounding the stock fuel sender to the inside of the cab. So on the stock sending unit on top of the gas tank there are two tabs. One tab goes to ground the other tab connects to ez wire that goes to the gauge. I’m going to scratch can to get a better ground. And remove the sender from the tank and move it to see if I get a different reading on my gauge
thanks
jerry
thanks
jerry
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More Turbo
Joined: Sep 2011
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Ok I checked the ground from the tank to inside the cab. I sanded so I got bare metal and reinstalled ground wire back to tabs on sender on top of gas tank. Nothing happened. Took off runts to positive side of gauge. Started truck and blew the fuse. No matter what I do the fuel gauge measures 1/8 tank. Battery connected or not 1/8 tank. I’m leaning towards bad fuel gauge.
thanks
jerry
thanks
jerry
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
To test the gauge, touch the sender wire to ground with the switch on. The gauge should move to full. If so, then the gauge is good and the problem is either the sender or wiring.
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Logistics Pro
Joined: May 2010
Posts: 3,793
Likes: 19
From: Austin
Hey Jerry,
We had problems with our gas Gauge reading as well. You don't say what type of gauges you are running &
the Sending Unit in the tank? If you have replaced the original gauges or sending unit with a more modern set up
you will need to think through the Ohms requirements.
In our case we were using Autometer Ford Classic gauges & a '70 Mustang tank sending unit... not compatible.
Our modern gauges had a range of 0 ohms full to 200 ohms empty. Our sending unit was sending 11 ohms full to 70 ohms empty.
We had to replace the sending unit with a universal one that used the same ohms as our gauge. All happy & working together.
Good luck over there.
Ben in Austin
1950 F1
We had problems with our gas Gauge reading as well. You don't say what type of gauges you are running &
the Sending Unit in the tank? If you have replaced the original gauges or sending unit with a more modern set up
you will need to think through the Ohms requirements.
In our case we were using Autometer Ford Classic gauges & a '70 Mustang tank sending unit... not compatible.
Our modern gauges had a range of 0 ohms full to 200 ohms empty. Our sending unit was sending 11 ohms full to 70 ohms empty.
We had to replace the sending unit with a universal one that used the same ohms as our gauge. All happy & working together.
Good luck over there.
Ben in Austin
1950 F1
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Thread Starter
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Joined: Sep 2011
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Well i replaced the fuse and guess what the fuel gauge registered. But the only problem is that I have half a tank and the gauge reads full. Should I test the sender outside of the tank. And also the fuel sender is stock and so is the gauge.
thanks
jerry
thanks
jerry
Cross-Country
Joined: Apr 2009
Posts: 84
Likes: 2
From: Holly Springs, NC
Check the signal wire isn't worn through or pinched somewhere and grounding out, because if it is you will get a perpetual full signal , regardless of what happens with the sending unit. Good luck .
Mountain Pass
Joined: Jul 2015
Posts: 225
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Ok, just got a new unit gauge and sender from Mid Fifties, connect wire to sending unit out of tank and gauge responds, put the sending unit in tank with at least half tank and it won't read more than 1/4 tank at most. Looked in tank don't see a baffle that interferes with float. Saw where someone said float was rotating but mine is fastened fast in the sending so it can't turn. As I said, with the unit out it seems to register and work correctly by manually moving float up and down but not in the tank.?????? Any suggestions appreciated...thks!
Lead Driver
Joined: Apr 2002
Posts: 8,813
Likes: 13
From: Littleton, New Hampshire
Make sure the sender is properly grounded. I had to run a wire from under one of the mounting screws to a ground for mine to work. Some tanks are insulated from ground with rubber insulators under the tank which interfere with getting a good ground.