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Hey gang. Working on my 23rd series instrument cluster. I did some painting of the dials, replaced some nasty wires, and I replaced my temp sender with an NOS unit - works perfectly. Oil pressure and ammeter gauges work perfectly, too. My fuel gauge, on the other hand, is shooting up to full, regardless of being connected to the sending unit - the feed bridge on the right terminal is connected. With the feed bridge disconnected, the gauge is lifeless (as you would expect).

This is also of course with the key turned to the accessory or run positions. It settles back to E when you turn the switch off.

Did something just fail internally on the gauge or is it possibly shorting somehow? I did reinstal all the cardboard disks, and I also remade the paper gasket that goes around the instrument cluster. To the best I can tell, none of the gauges are touching. It worked fine before... what am I missing? Thanks, all.

The sender has two little leaf springs in it. One of them can fall off and perhaps short it internally. Either way it seems like it must be shorted somehow….

Hey PGH - just making sure, did you mean the gauge has those leaf springs?

Since the gauge moves to full scale when powered and drops back when off it sounds as if the basic gauge internals may be OK. Since you worked with the terminals and cardboard insulators, if there are no wires connected to the sender side it also sounds like there may be a short to ground somewhere on the sender side terminal. Since nothing smoked with ign on the BAT side sounds OK. If there is a direct short, don't leave the gauge powered on for very long in this condition or the gauge could burn out.

48-56 gauges are all the thermal type which means a thin wire heater element is wrapped around a bimetal strip. Each side of the heater connects to a terminal. When the heater warms the bimetal strip, the strip bends and one end being fixed and the other attached via a pivot or linkage moves the needle. Here is a photo of a 56 gauge showing the typical thermal gauge internals. 22-23 series gauges will be very similar in construction but do use a different type sender controlling the heater so gauges operate slightly different electrically.




In the second or angled photo of these external views of a 22-23 series gauge you can barely see under the cardboard to where the terminal passes thru the center of a larger hole in the metal case. The long heavy strip of cardboard holds the terminals and is also fastened to the case. Being very stiff, it keeps the terminal rigidly upright and positioned in the middle of the hole so nothing can touch the case. Is there any chance the cardboard was loosened and now something has moved or was damaged on the sender terminal side so the terminal is now able to touch the case? If that is OK is there a chance the terminal was twisted in any way so the wire connecting terminal to the heater element could have been pulled and shorted.

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Howard, thank you so much. Definitely have some clear things to chase. I'll keep y'all posted.

The experiments continue. The gauge works just fine when I isolate it from the cluster. I can replicate the racing-to-full dial by shorting the sender terminal to ground. I just have no clue what the terminal is interacting with when it's in the cluster and behind the glass. Wires are free and clear of the space behind the terminals, and there are no exposed wires. So far, the jumper from ground to the sender terminal is the only way to make the gauge race to full.

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Check the area where the gauge contacts the cluster and where the screws go. It’s possible that a screw is shorting against a wire somehow.

One time I was working on an industrial motor that had a short in the stator that I traced to someone using a replacement screw of the wrong length. It was the exact wrong length to seat completely at the outside yet wear away the varnish of one of the stator wires internally.