Which guage or both ?
redfish, checking the schematics in both the 1977 and 1978 Dodge factory service manuals, neither of them shows any "external (ammeter) shunt".
If you're looking for a nice little black box under the hood labelled "AMMETER SHUNT" (or a similar box on the wiring diagram) you're going to be looking a long time, unless you're looking at a cop car or taxi originally equipped with a high-amperage alternator. Those got separate external shunts, such as the one called out in group 8-37-5 of the '74 FPC for Satellite/Coronet with certified speedometer (i.e., cop cars):
On non-cop cars, a section of the main charge feed wire is used as the shunt. Good, solid info on both types of ammeters in Mopars
here on RamCharger Central; keep in mind trucks switched to external-shunt ammeters later than passenger cars. The whole post containing the highlighted text (at the link) is worth reading. My '89 D100 had an external-shunt ammeter. A broken one, but an external-shunt unit nonetheless! :-)
Bill, I respectfully suggest you spend a little less time being adversarial on the internet without having all the facts, and a little more time examining the ammeters and main charging circuits in '76 versus earlier-year A-bodies. Also spend a few minutes reading the '71 and '76 Chrysler new-engineering-features books which have extensive descriptions of the move to external-shunt ammeters ('71 except A-bodies, '76 in A-bodies). I'm in the middle of an office move, but when everything's all unpacked on the other end I'll be happy to scan in the relevant pages for you, if you haven't found them elsewhere by then.
In the meantime, this is a '76-only A-body ammeter:
And this is a '70-'75 Valiant/Duster + '72-'75 Dart ammeter:
From the front (gauge face) they look identical, but from the back and underneath they look pretty different, eh? The brass-strap frame on the '70-'75 ammeter serves as the shunt. That's where all the current goes through. The later ammeter is a totally different design; the minor current going through the large coil of wire is what moves the needle, and we see an insulating frame rather than a conductive one, because all the system current does not go through the later ammeter.
Additional discussion of internal- vs. external-shunt Mopar ammeters is
here.