Re: [AMC-list] fuelgage-tempgage stopped woking

[Frank Swygert <farna@xxxxxxx>]

Matt's spot on, again! The only other possibility is that the pin sending 12V to the gauges is corroded and not allowing voltage to pass, or the wire is broken, or the trace from the pin to the gauge. All easy checks. 

I have heard of someone disassembling the gauge and replacing the old bi-metal voltage regulator with a solid state, but haven't done it myself. Looking at the TSM, the fuel gauge has three terminals. They are marked "A" (~5V out from regulator -- goes to temp gauge), "I" (12V input), and "S" (out to sending unit). To get the temp gauge working you can simply take 12V from I, go to an electronic regulator, then connect the 5V output to A. That MIGHT even get the fuel gauge working. Since the gauges are totally dead I'd have to say that there is no connection in the built-in bi-metal regulator at all, and the above should restore both gauges. 

The bi-metal regulator is an "averaging" regulator. It delivers an average of 5V by quickly switching the 12V power supply on and off. It does this by heat. The bi-metal strip heats and bends, breaking contact, cools and snaps back shut. It does this many time a second, creating an average output of 5V. The gauges don't care if they get an average or constant 5V, they work just as well either way. The bi-metal strip has probably broken off inside the regulator, or it has frozen in the open contact position. You might want to pull the gauge cluster and that gauge, then see if it will shake. Don't want a loose strip in there to short anything out. If it starts working again it could short out an attached electronic regulator also. Really need to go into the gauge and make sure the strip is removed or fixed so it won't move. Since you have an offer from Mark (wrambler) for another, you might want to disassemble yours and see if you can make the hack work. 

-------------------
Date: Fri, 01 Jan 2010 16:17:36 -0500
From: Matt Haas <mhaas@xxxxxxx>

When both stop working at the same time, that's usually a sign that 
voltage regulator is shot. The factory fix is to replace the fuel gauge 
but those can be hard to find. You may be able to replace the mechanical 
voltage regulator with a solid state version but I'm not aware of anyone 
who has done this to this type of regulator. Tom Jennings has a page at 
http://wps.com//AMC/dashreg/index.html that describes what he did for a 
car that has it as part of the circuit board.

Another alternative is to check with places that repair gauges and see 
if they can fix yours. AMC used Stewart Warner gauges so hopefully, the 
guts aren't all that much of an oddball.

--
Frank Swygert
Publisher, "American Motors Cars" 
Magazine (AMC)
For all AMC enthusiasts
http://farna.home.att.net/AMC.html
(free download available!)


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