Joined the forum today, but I've been reading awhile now. The info available here is priceless. The 54 Customline in my avitar is new to me as of end of Feb. I rewired with a painless kit. Now I'm working on, why won't this work issues. Primarily water temp and gas gauges. But that's the joy of old cars, right?
I'm not as sure on cars produced after the flathead era but many FoMoCo products used King Seeley current based systems for fuel quantity and coolant temperature. If a person replaces the senders with a different resistance based part then it won't function like it should. The replacement parts for the KS senders are crap for the most part. The original parts were very reliable and last a long time but good NOS or used ones are getting harder to find. If a person changes them over to resistance type systems then the indicator should also be changed to match the resistance level for proper calibration and accuracy of the system. If a car had an oil pressure gauge then it also may be affected but many just have the warning light.
orangedog,
A couple diagrams of the fuel gauge circuit and hardware to help explain the differences.
Image 1. The pre '57 King/Seeley setup.
It uses bi-metal contacts in both the Sender and Gauge to create the current flow & heat that moves the gauge needle.
You can see by their design that they are not polarity sensitive.
The oem gauge and sender pairs are generally not voltage sensitive either, as the heat/bi-metal contact design is self-limiting in current flow.
Image 2. The '57(+) fuel gauge.
It uses a variable resistor in the Sender instead of bi-metal contacts.
I suspect the gauge & sender parts for '54 and '55 are the same.
In '56 the gauges, senders and their electrical specs were slightly redesigned for the change to 12 volt systems, and are one-year-only parts.
The '56 Senders may look the same as the earlier ones but aren't, with any luck they're marked "12v". photo 3
The dashboard gauges in full-sized Fords changed in appearance for '56.
In '57 the gauges and senders were re-designed again; in physical size, appearance and electrical specs.
Individual parts from each group won't work correctly with parts from the other groups. And as
rotorwrench mentioned, the individual "new/replacement" style parts rarely work if mixed in the same circuit with oem or nos parts.
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