Anyone here know of any reason why a NOS gas guage and NOS sending unit will not read correctly? I am trying to test it out of the car before going through the trouble of installing it. at 6.2 volts it will read empty and at 6.3V it reads full.
I have looked at the wiring schamatics and I cant see reason why its doing what its doing.
Anyone have any ideas?

Are you sure you are connecting the sending unit resistor in series with gauge and power-source? If so, what are you using for the power-supply?
Is the sending unit outside the tank, so you can move the arm? Does it react differently if you move the sender-arm, with about 6.v applied?
I remember someone mentioning that some years had a voltage limiting regulator mounted at gauge that limits max voltage at gauge, but don't know if your's has that or not?

I have a variable power supply so I can adjust it to whatever I need for 1-16 volts. Everything is being tested outside, positive gound hooked to sending unit flange wire hooked to sending unit stud going to guage and negitive hooked to other stud for power. there is no power drop resistor on my car now and none that shows up in the wiring schamatic, also tried dropping the voltage to 3 1/2 and worked it up 1/10 volt at a time and still the same results.

Back to Rick's question, if you set the voltage at 6.3 volts, and then move the sender arm though it's range what does the gauge do? What does it do if you do the same test at 5.0 Volts.

The sender works on resistance as the arm moves.

You didnt not tell us what year of Packard you are reffering too. But most post-war Packards have a voltage regulator that is installed on the back on the dash cluster that keeps the voltage at constant 5volts (yes 5 volts, not 6). This exact same voltage regulator was also used on the 55/56 12v cars also (same part number). So no matter if it was 12volts or 6volts, the output is 5volts to the gauge and then on to the sender.

Hope this helps.

The car is a 41 120, The guage no matter what voltage is either empty or full when moving the float arm up and down. I looked at the back of the guage panel in the car and there is no voltage drop resistor or regulator on it I also have 2 more guage panels out of the car and there is no place for one. most american made cars used voltage regulator on thier guages so they could keep 6 volt guages until the early 70s, I belive ford was the last to redesign thier guages to work on 12 volt.

My 1990 Mustang used a voltage regulator to reduce to six volts. It is a little PC board that snaps into a slot with four contacts, mounted behind the speedometer. Six volt gauges are very common on modern cars.

My '55 Customline's fuel sending unit has a contact, current limiter, and bi-metal strip inside. Power starts at the gauge and on to the float unit, then to ground. The float arm pushes on the bi-metal strip to vary contact cycles. There are NO resistors, NO dash regulator, and my system is 6-Volt, pos. gnd.

Yours might use the same technology. Using a VOM is very confusing because the sending unit contact is either closed, or it's open. Again, there is no rheostat or variable resistor, just current heating a bi-metal strip (kinda like your turn signals, only a lot less current).

With a full tank, the contact is constantly closed, pegging the dash gauge. At half full, the contact is open and closed in equal cycles, making the gauge read 'half.' When the tank is empty, the contact is always open, no current flows through the gauge, and the pointer rests at, 'EMPTY.'
Check it out:

Note the snail-cam inside for adjusting "1/2 Full" scale. It pulls (sets) the top contact higher or lower, adjusting contact closure frequency.

I couldn't believe what I was seeing when I first opened this sending unit. No wonder they went to a cheaper rheostat. Cold ambient temperatures tends to show more gas on this setup. By the way, that current limiting resistor corroded, causing this unit to fail (open). Hope this helps. - Dave Dare

Have you tried hooking an ohm meter up to the sender and moving the arm though its range. You should see a increase when the arm moves down. I have an old sender that reads around 20 ohms when the tank would be full and about 120 ohms when the tank should be empty. I would not use these number as a sure setting since this is from a 1947 Super Custom Clipper and it still needs to be cleaned up. But this should give you an ideal what to look for. I'd look at the sender as being bad, new parts have known to be bad. The reason I would say the sender is that it looks like the sender is not connected to ground, or as most people would say you have an open circuit. But I'm only troubleshooting this from what I've read. So the first thing I would check is the sender.
Good Luck!
Wes

Are you grounding the gauge case as well as sending unit? I believe 41 used opposing magnet S-W type units where needle is balanced between 2 electromagnets. The battery supplies both coils where there is a more or less constant magnetic field on one being influenced by another coil that is controlled by resistance in sender. It sounds like the fixed field is not there, which if gauge is not grounded would be the situation. There is no regulator used on those units as any supply variation is felt equally on both coils and compensated for.

I have used an ohm meter on the sending unit and it does read like you said 20 ohms full and 120 empty, and the fuel guage is the Stewert Warner type. both guage and sending unit are grounded when testing. Maybe I just have a bad NOS guage.. I will take it apart and see whats up, I have an uncle that can rebuild the guage if its needed.
Thanks for the picture of the inside of the Ford sending unit, looks just like the one I just replaced in my 48 Lincoln conv. coupe.

My 38-39 Packard shop manual shows the sender to work on the twin coil setup as described earlier and the sender is just a variable resistor to ground. I don't know what the range of the resistor is.

Good call HH56, I just got though looking in my Motors Auto Repair manual, and both the gauge and sender should be grounded.

Wes