frank's more of a help here than I am.
Not that it should matter much but lets see if you can explain what you've got here. yes no is fine
This is a 12 Volt battery powered system. Yes
Battery positive is connected to the engine block or head.yes
Battery negative goes through an on/off switch to the coil negative.yes
Flip the power on (or connect the wire) and the coil positive shows 12 Volts. Yes
Coil positive leads to the points.