Gas guage reads backwards on 1956 Thunderbird

[metallic]

Make sure you have the battery installed properly. Some cars will run with reverse polarity but won't charge etc. My first job at a Ford dealership in the mid 80s was to fix a reverse polarity issue on an old Dodge I believe. I think they ran positive ground unbeknownst to the owner.

Battery cables are installed correctly. This does run positive ground.

[428PI]

Perhaps your gauge is for negative ground? Did it ever work properly?

[metallic]

Perhaps your gauge is for negative ground? Did it ever work properly?

Not since I owned it for about 3 years

[HKS]

The restorer is Ted Rossi of Westminister, Co. The wires were reversed on gauge and no help.

This points to a fuel tank sending unit being reversed. Or wrong part.

[Jimr]

Shop manuals say 3.0 volts across the 56 or 57 gauge (dash unit) and in each case the needle should read approximately half scale. this can be achieved by using two 1.5 volt batteries. By shorting the wire at the tank to ground the gauge should read full. This being said the sender should have zero resistance in the full ( or all the way up) Position .
Putting 6 volts to the gauge should pin the gauge. If it doesn't in my opinion the gauge is wrong.

[metallic]

Shop manuals say 3.0 volts across the 56 or 57 gauge (dash unit) and in each case the needle should read approximately half scale. this can be achieved by using two 1.5 volt batteries. By shorting the wire at the tank to ground the gauge should read full. This being said the sender should have zero resistance in the full ( or all the way up) Position .
Putting 6 volts to the gauge should pin the gauge. If it doesn't in my opinion the gauge is wrong.

I will discuss all these good responses with my mechanic and see if we have missed something. Thanks

[HKS]

Shop manuals say 3.0 volts across the 56 or 57 gauge (dash unit) and in each case the needle should read approximately half scale. this can be achieved by using two 1.5 volt batteries. By shorting the wire at the tank to ground the gauge should read full. This being said the sender should have zero resistance in the full ( or all the way up) Position .
Putting 6 volts to the gauge should pin the gauge. If it doesn't in my opinion the gauge is wrong.

Jim,
Would there be a resistor in series with the sending unit dropping the 12 volts to 6? The 56 and 57 Tirds were +12V negative ground. The resistor would make the sending units compatible with 6 and 12 volt systems (12V with resistor and 6V without).

HKS

[Jimr]

Jim,
Would there be a resistor in series with the sending unit dropping the 12 volts to 6? The 56 and 57 Tirds were +12V negative ground. The resistor would make the sending units compatible with 6 and 12 volt systems (12V with resistor and 6V without).

HKS

The sending units are different for 6 volt and 12 volt

[HKS]

The sending units are different for 6 volt and 12 volt

That is true, but a fuel tank repair project may have used whatever parts were available.