[mf_luder]

I appreciate the response. I know how the ammeter works and I know how the alternator works. There's nothing in that other thread that's new to me. You're right that I got the gauge of the wire wrong. I was reading it from a diagram that I thought was accurate, but I've looked at mine now and it's 12 AWG. I was briefly confused about how you might have got the idea that I thought alternators produce their maximum output all the time (I don't know why I'd use the phrase "maximum output" if that were the case), but I assume it's because I mentioned that I think the shunt resistance should be adjusted to account for the new alternator. I said "needs to", but I know that it probably isn't strictly necessary. I do think it's a better idea to do it than not to do it, but I can't do it either way without knowing the original shunt resistance.

To be clear, when I say that the truck doesn't have its original engine, alternator, or wiring harness, I don't just mean that they've been replaced; I mean that that they are not even remotely the same as they were originally. The wiring harness is one that I've designed and built from scratch, and its power distribution scheme is completely different. I have what's left of the original harness dissected for reference, which is how I know that the original shunt wire is in fact 12 AWG, like you said, and that it's a little bit less than four feet long. I know that you can buy complete harnesses, but I prefer to build my own, not least of all because a lot of the original routing no longer makes sense. As you know, the external voltage regulator was originally next to the horn relay on the driver's side of the radiator. Obviously, it was placed there because the alternator was on that side. With the alternator moved to the other side, next to the battery, and the external voltage regular gone, there is no reason to run a 10' wire around the driver's side of the radiator from the alternator to the battery. The horn relay bus will no longer be used. That leaves me with the need to find a replacement for the shunt wire that's not four feet long, because the alternator's battery wire is going to terminate about a foot away from the positive battery terminal and I think bundling up three feet of extra wire and zip tying it to something is an ugly solution. I'd rather have a real resistor and it's time to buy it because I'm trying to get that part of the harness finalized.

Using one of the resistance charts you mentioned seemed like a good idea to me as well, and according to those charts the shunt wire will have a resistance of 4 to 6 milliohms (let's call it 5), which would produce 0 to 275 mV with a 55 amp alternator, as I believe the truck would originally have had, or 0 to 315 mV with a 63 amp alternator. The problem with that is that the resistor pictured in the thread that you linked to, which is from a Chevy II from the same era that used a real resistor, is supposedly about 40 milliohms, which at 55 amps would produce 2.2 volts (I could easily be wrong about that. That seems extreme). Modern automotive ammeters seem to take about 75 mV most often, and sometimes 50 mV. These calculations seem to indicate that the ammeters in these trucks were very different than the ammeters in the Novas that were made at the same time, and for that reason I'm not confident that they're right. As I mentioned before, it's not cost effective to buy a resistor that will produce 50 mV and keep replacing it until I get the result I want, and I don't know how else to be sure that I don't fry my gauge. I don't trust those charts enough to put 300 mV across something that is maybe only designed for 50.