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Old 04-02-2008, 10:23 AM
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Default Is it possible to "fry" your ammeter gauge?

So last weekend I was troubleshooting my faulty fuel gauge and pulled the instrument cluster out of my 40. The good news is that I found a short in the fuel gauge wiring and I'm pretty sure its fixed. The bad news is that I touched the hot lead on my ammeter gauge to the dash panel for a second or two, and (after a spark shower and some electrical smoke) now I think that gauge is not working. It used to be "lively", and bounce around when the truck was running. Now it just sits there and never moves.

I couldn't see anything obviously damaged, but then again, I don't remember what it looked like before "the incident."
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Old 04-02-2008, 10:33 AM
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I don't think shorting out the hot lead would fry the gauge, as the power should come straight from the battery to the hot lead. I can't remember if there's a fuse (I don't think so), but you might have melted some of the wiring. Try and trace it back to the battery, or put an ohmeter on it, to check it. Mine usually jumps around when I first start the truck as the battery is being charged, but after a while it gets to the point where it doesn't move much. A quick way to check is to watch it (engine off) when you turn the headlights on and off - it should jump back and forth.

Oh and disconnect your battery next time you pull the gauge cluster
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Old 04-02-2008, 11:06 AM
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I know - but there was a lot of trial and error, and I guess I forgot one time to disconnect the battery
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Last edited by Jacket; 04-02-2008 at 01:02 PM. Reason: misspelling
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Old 04-02-2008, 11:42 AM
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The ammeter in your FJ40 is really just a voltmeter in parallel with a shunt resistor. If you know the exact value of the resistor, then the voltage across it is the current. Remember Ohm's Law, V=I*R => I=V/R. IOW, 15A produces 15V across a 1 ohm resistor, 40A is 20V across a 0.5 ohm resistor, 10A is 1V across a 0.1 ohm resistor, etc.

Attachment 8505

What that means is shorting the (+) side of the ammeter to ground just completely bypasses the ammeter and shunt. Most likely you melted wires and the reason your meter isn't working is a bad wire someplace. Like Subzali says, trace the wiring I bet you find one that is melted or burned up.
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Last edited by DaveInDenver; 08-26-2010 at 10:16 AM.
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Old 04-02-2008, 01:09 PM
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Figures.... I had so much fun tracing the wires for my fuel gauge, why not do it again?

Thanks for the info.
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Old 04-02-2008, 01:38 PM
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Quote:
Originally Posted by Jacket View Post
Figures.... I had so much fun tracing the wires for my fuel gauge, why not do it again?

Thanks for the info.
It could be worse.

First, it's much simpler under the dash and hood on your 40 than the Tacoma. Second, well, it'll be the one that's black and charred...
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Old 04-02-2008, 01:43 PM
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When I burnt my CJ5 to the ground on Holy Cross, I shorted my ammeter

If you look on the high lift you can see the entire electrical system that had to be replaced. I am sure glad I brought the spool of red wire with me.

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Old 04-02-2008, 02:02 PM
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Who's Cruiser is that behind you? IIRC you sold the CJ right after you got back, and then came over from the darkside not too long after right?
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Old 04-02-2008, 02:55 PM
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Nice chrome bumper there, Root.
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Old 04-02-2008, 02:56 PM
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That's OEM on J**Ps, that's why the Cruiser gods degraded them from off the factory floor. By the time AMC caught on it was too late...
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1996 FZJ80 1FZ-FE factory lockers + Safari Turbo , CDL switch, cup holder, Metric TLC leather, heated seats and JDM switches
2000 Tundra Limited TRD 2UZ-FE SOLD
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