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I recently found a set of gauges from a '57 GMC that I would like to use in my '54 GMC panel truck, since they are already set for 12 volt operation, if I remember correctly.

Two questions:
1) The water temperature gauge is electrical, not the capillary tube style that is original to my '54 (this is good, I am putting in a later 6, and I have no idea if the old tube gauge works, anyway). What kind of sender does this gauge use? Is there an aftermarket unit that will work?
2) The fuel gauge has the usual two terminals on the back, but there is a wire-wound resistor type of thing on the back (it looks original, not like a voltage-dropping resistor), that has a '30' stamped on it near where it connects to the right-hand post (looking at it from the back). The other end of the resistor-type item is held up by a bracket that is attatched to the left post, but they are isolated by the bakelite frame for the resistor. This appears to be a three-wire connection, how does it connect to the electrical system and the tank level sender? What is the operating range of this gauge (0-30 ohms, 30-90 ohms, or something else)? The 'resistor' is broken, can I get a replacement anywhere? The usual vendors' online catalogs didn't have anything like it listed. I have a 2-contact Stewart-Warner 12v fuel gauge that was in the truck when I bought it, would I be better off adapting its internals to work in the GMC gauge?

Lets do last question first. The 12 volt dash gauge is calibrated to work with a 12-volt sender which works in the range of 30-90 ohms. By contrast your original 6-volt sender worked in a range of 0-30 ohms. So if you change the dash gauge, you will also need to change the sender as well.

As for your temp gauge that is likely the same story. One alternative is to install a Runtz inline to each gauge. That way you can keep the original senders and dash gauges and everything will work as they did originally. Its kind of related to the kiss principle.....Thanks Randy

The truck will have a TBI fuel-injected 250 in it when finished, with a modern GM truck gas tank, so the 12v sender is not a problem. It's a panel truck, so the tank is fairly rare, and the one on it is totally clogged with rust. The modern baffled tank with high-pressure in-tank pump will work better for this job, anyway.

Does anyone know if GM senders were still 30-90 ohm units in the late '80s and early '90s? I think an S-10 pickup tank will fit perfectly in place of my original.

My truck has the capillary-tube style water temperature gauge connected to the old 248, so there is no sender for that. Does anyone know the resistance range of a late '50s temperature sender vs. something that will work on my 250 I6?

I remember reading about a rebuilder for capillary temperature gauges. Anyone with a referral?

For a GMC 55 ist series