Koehler MV20 battery charging issue

I just replaced the Briggs 12hp on my 30inch Snapper mower with a new Kohler MV20. (The Kohler has been in storage for 28 years in the original box.)

I don't think the battery is charging. The Kohler has a regulator with three wires. The Briggs did not have a regulator. I removed the diode from the Briggs stator and installed the diode on the purple wire on the Kohler that charges the battery.

I am wondering if I need to remove the diode?