Found the small black wire connection. It's connects to the body of the switch in the start position. It's a ground.
The ignition switch for a '78 Volare works for a D100 or D150 from 1978-1987, so I went looking for wiring diagrams for those since I can't find one for the Volare. Found this website with a zip file labeled "1979 Dodge & Plymouth Truck / Ramcharger or Trail Duster" -
MyMopar - Mopar Forums & Information - Mopar Wiring Diagrams
The schematic shown on page 22 seem to match ok, minus some wire color differences.
Interesting thing is, this is for a truck without lean burn. It uses a wire off the starter relay to up the power on the coil during starting, but doesn't appear to care that IGN1 is still powered.
