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I am trying to figure out how to get my fuel gauge to work, in short I have 12 volts to gauge and from the gauge to the sending unit which also has 5-6 volts and my understanding here should be no voltage at the sending unit. No matter how it is wired I still have voltage at the sending unit. It acts as though the unit is always grounded because it goes straight to full, it will not go to empty when moving the float. it stays full. I am confused, anyone with a little help, thanks in advance.
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fuel system
- Thread starter rogerzipp
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Lots of times installing a separate ground wire between the top of the sender and the chassis does the trick.
The sending unit is a variable resistor between the gauge and ground.
You can also test by running a separate wire from the "T" terminal on the back of the gauge to the terminal on the sending unit.
The sending unit is a variable resistor between the gauge and ground.
You can also test by running a separate wire from the "T" terminal on the back of the gauge to the terminal on the sending unit.
I have added a ground to the sending unit and attached it to the chassis of the car and this does nothing, I have ran a separate wire from the gauge to the sending unit and stays the same. when I read from the terminal on the sending unit to ground and move the float my resistance varies from about 69 ohms full to about 15 ohms empty.
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The last thing you could do is to make a bench setup using a 12V DC source (battery), the gauge and the sender.
Addendum: Test circuit: Battery hot lead to "B" terminal on gauge; gauge "T" terminal to sender terminal; ground on sender to ground lead on battery.
Move the sender through its arc and see if the gauge moves accordingly. If not, one or the other needs repair. I had a similar situation and sent my gauge and sender to APT in Minnesota - now The Gauge Guys. I had a broken wire inside the sender or gauge (forget which) - they fixed the two to work together.
See:
https://www.gaugeguys.com/
If the gauge-sender combo works on the bench, the problem is in your car's wiring.
Addendum: Test circuit: Battery hot lead to "B" terminal on gauge; gauge "T" terminal to sender terminal; ground on sender to ground lead on battery.
Move the sender through its arc and see if the gauge moves accordingly. If not, one or the other needs repair. I had a similar situation and sent my gauge and sender to APT in Minnesota - now The Gauge Guys. I had a broken wire inside the sender or gauge (forget which) - they fixed the two to work together.
See:
https://www.gaugeguys.com/
If the gauge-sender combo works on the bench, the problem is in your car's wiring.
Randy Forbes
Yoda
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It's also possible, as Steve alludes to, that the (green w/black?) wire FROM the sending unit is grounded somewhere along its path.
Try connecting a separate, short piece of wire between the terminal on the sender and the terminal on the gauge; make sure you connect the sender to chassis ground also ("alligator-clip test leads" are great for this). You can then perform the test with float/sending unit in hand while sitting in the driver's seat...
My own gauge/sender has issues too, but I rarely get the pleasure of working on my own car (
) I'm hopeful to correct that situation before too much longer (I'm 62-1/2 darnit, time for people to stop mailing me their cars...). Instead, I just keep the twenty-eight (28!) gallon tank 1/2-full or better, and keep driving 
Try connecting a separate, short piece of wire between the terminal on the sender and the terminal on the gauge; make sure you connect the sender to chassis ground also ("alligator-clip test leads" are great for this). You can then perform the test with float/sending unit in hand while sitting in the driver's seat...
My own gauge/sender has issues too, but I rarely get the pleasure of working on my own car (
) I'm hopeful to correct that situation before too much longer (I'm 62-1/2 darnit, time for people to stop mailing me their cars...). Instead, I just keep the twenty-eight (28!) gallon tank 1/2-full or better, and keep driving
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All these ohms are confusing.
What Randy describes is simple: as you move the sender arm from its empty (down) position to its full position, you should be seeing the gauge needle move from empty to full.
Based on your descriptions, it sounds as though the sender might be doing its job, but the gauge not reading it - possibly a broken wire internally in the gauge. The internal wires are hair-thin and easy to break. I know this from fumble-fingered experience.
When you're doing this test, suggest connecting a third jumper wire from the float arm to the sender chassis. There can be an intermittent connection between the sender arm which contains the brushes and the resistor coil on the sender chassis side. You might also connect a fourth jumper from the gauge center mounting screw to a chassis ground.
see Charlie Hart's fix:
https://www.healey6.com/Technical/Erratic fuel gauge.pdf
What Randy describes is simple: as you move the sender arm from its empty (down) position to its full position, you should be seeing the gauge needle move from empty to full.
Based on your descriptions, it sounds as though the sender might be doing its job, but the gauge not reading it - possibly a broken wire internally in the gauge. The internal wires are hair-thin and easy to break. I know this from fumble-fingered experience.
When you're doing this test, suggest connecting a third jumper wire from the float arm to the sender chassis. There can be an intermittent connection between the sender arm which contains the brushes and the resistor coil on the sender chassis side. You might also connect a fourth jumper from the gauge center mounting screw to a chassis ground.
see Charlie Hart's fix:
https://www.healey6.com/Technical/Erratic fuel gauge.pdf