I Have a late model 140 (with electrical issues)
With mine, it used to have 12v on one resistor terminal that fed the coil when cranking. When you released the key the resistor I think did supply the current to the coil thru the same wire.
On second thought - your alternator does not have the ground wire from that same bolt (resistor mounting bolt) that runs to a ground on the right side of the engine.... you can try runnning a jumper wire from the bolt to the ground bolt. If the alternator is coming ungrounded - it can cause the same effect you are having.