I'm brand-new to this site as a member; but, have been lurking for several years now.
I've done extensive work on my own 55 Crown Vic engine temp & fuel guage senders which both work on the same principle.
Both sender AND guage have bi-metallic heat-sensitive 'motors' in them along with resistance wire wound around the 'motor' elements. The engine temperature 'influences' the sender bimetal 'motor' position, which influences the long-term-average current through both the sender and guage, which then heats the guage 'motor' to the appropriate calibrated position. The fuel guage works similarly in that the fuel tank sender position 'influences' the sender bimetal 'motor' position, which acts identically on the fuel guage as the engine temperature guage explained above.
These senders & guages are matched-pairs, and cannot be used with any other senders or guages! They will not work seperately!
IF YOU KNOW WHAT YOU'RE DOING, both the senders and guages can be re-calibrated; I have done just that; but, they must be matched, and you must completely understand the operating principles involved (I have an electrical engineering background - not working int he field now, am a 'Ham Radio operator', previous TV broadcast transmitter engineer, etc. who has been involved with this 'stuff' since about age 6 or 7.
Both the heat sender and the fuel tank sender have calibration screws; and, both guages have two calibration screws each: One for 'zero' adjustment (which is extremely sensitive and very painstaking to 'get right', and one for 'full-scale', which is easier to adjust; but, each is interactive with the other! So, you must go back & forth betweent he two many times.
If you should try any adjustments, PLEASE scribe the initial starting points before making ANY adjustment trials so that you can at least get it back to where it was.
These sender/guage systems are a full 6-volts for original 1955 units; and, are connected in series between the battery posts (use a 6-volt motorcycle battery for 'shop' adjustments).
I hope that this will help.
Thanks, JLB
55 Ford Crown Victoria Steel Top