John,
You need to make up a new wire going from the male spade tach output on the MSD box directly to the tachometer. The green wire should be dead and not connected to the coil or the tach or the MSD box.
This is totally optional, but I usually hook up the black wire on the MSD box that normally is connected to the coil to the green wire running from the tach to the coil. This eliminates running extra wires through the firewall.
This should work, if not we'll try something else.
