Positive Battery Cable Connections for 71 340 Demon

The black cable should connect at the small stud at the starter and at the "square screw" connection on your starter relay

The extra, smaller red should connect to the "big stud" on your starter relay

And ALWAYS remember---black is not necessarily ground. It is NEVER ground in AC wiring, and "sometimes" not ground in other / auto wiring. (The output of your alternator is black)