On the actual gauge itself, where the copper support makes a 90 degree turn to support the pivot for the needle, it's all charred and looks like there's a hole drilled in the middle of it, right at the bend. I'm assuming this isn't normal, as I don't remember seeing any evidence of burning when I pulled apart the instrument cluster on the in the ex's Dart. It's still intact, but there is definately a small amount of material missing. Is is still safe to drive until I can bypass it and install a voltage gauge, or should I park it and try to track down the cause?

Also, while driving the car earlier today, the ammeter would peg when the engine was throttled up, but rest back at zero when idling. I'd never noticed this happening before, and I know the battery was low this morning when I checked it ('bout 10.5 volts). Nothing I did would move the needle either, ie; turning on lights, the fan, the wipers, etc. Is the battery having been low the cause of the high reading, or you guys think something else might be at play here?

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

AT 10.5 volts it sounds like you've lost a battery cell.

Don't drive with that battery. Try another one first.

At idle there the alternator doesn't have enough output to try to charge the battery.

Above idle, it's charging a 10.5 volt battery rather than a 12v battery, so it's pegging the ammeter

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

If the battery's good, then "pegs high with rev" suggests the regulator has lost its ground, internally or externally. There were some regulators (such as the MP "race" regulators ) that required the paint/coating scraped off the mounting base so they could ground. The drilled hole and burn/char marks aren't normal, so figuring out what's up or bypassing the ammeter by connecting its two leads together and carefully insulating them would be a good idea.

(But note, it sounds like you do have a dead cell in the battery, so go replace it first).

Ammeter vs. voltmeter is an old debate which doesn't necessarily have a single right answer. Those who claim there's a definite right answer to the question are not being honest. Spirited thread here.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'm heading back out now and I'll check all the grounds. I also noticed that there were also burn marks inside the metallic housing for the instrument cluster, leading me to thing that the current had been arcing. And from the looks of it, arcing for a long time. I had the battery tested today and it tested good. Bad cell was the first thing I thought of since my dad just had that happen with his POS Jeep. Anyway, I cleaned up the copper bend and coated it with solder so that it wouldn't cause a weak point in the system, and put two layers of electrical tape over the spot on the housing that it looked like it had been arcing to, so hopefully that'll help. If the grounds all check out, I'll swap in the battery from my truck and see if it keeps doing it.

As far as the ammeter Vs. voltmeter debate, I agree with you. I prefer a voltmeter, and whenever anyone asks me, I just chalk it up to personal preference.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me

Oh, then we disagree; I like an ammeter!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Fair 'nuf, fair 'nuf

I reinstalled the instrument cluster (after extensive cleaning and repair work), put in the battery from my truck, and it was reading about 5-10 amps positive. Tested everything to put on a load, and it would quickly drop and then recover to 5-10 amps positive, like it did before today. Poifect. So just out of curiosity I put the low battery back in and started it, and it was about 20-25 amps positive, but no where near pegged. I have a feeling the arcing to ground inside the cluster was a big factor in what was going on.

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'74 Duster w/ HEI ignition, beat to snot suspension, A904, 8.25" 3.55 SG rear, still being tuned up and gets 17 MPG

Know how they always build a better idiot? That's me