1968 Dart gauge help

WHAT YOU CAN DO in order to find a short, while not smoking anything in the harness:

Get yourself a big wattage 12V lamp, such as a stop tail lamp (1157) or an old headlamp which has at least one good filament

I use an old stop/ tail light socket because you can wire it different ways for different jobs.

Hook this large wattage lamp in series with the battery ground. Go around and be certain everything is "off" including truck lamp, dome lamp, glove box lamp, everything. The lamp should not light. If it lights dim, it shows some sort of drain. If it lights up bright your short is still likely active.

Remove/ disconnect items until it goes away. There is a VERY remote chance something is wrong with the headlamp switch, so try it as well. Don't forget the alternator "big stud"