Wiring in some gauges and a stereo.

73 Duster 360 said
I do know there is a hot and a ground powering the cluster connected to the back of the alternator gauge

Depending on year, The black and red on the back of the alt gauge are both power. One from alt, one from battery.

Your best bet is to get a free (mymopar.com) or buy (classiccarwiring.com) a wiring diagram for your car. Then start tracing.

You might want to think about buying a good used or new OEM style dash harness