Grant Erwin wrote:

So now the question shifts to: since my engine has been wired up
backwards for at least a decade, is there any hope of making the
generator generate again, assuming I rewired the system and battery to
6V positive ground again?
Is the generator also the starter? (I have a circa 1968 Wisconsin 12 Hp
that works this way). If so, and the generator/starter can start the
engine, it should also work as a generator for the intended voltage. it
may or may NOT work with the electronic regulator. Mine is a 12 V
system with a Delco generator/starter, and I figured out what was wrong
with the regulator. It had no arc suppression on the voltage regulator
points! I added a small capacitor-resistor in series combination and it
has worked great and held adjustment since then. Before, the points
burned up so fast it needed a charging voltage adjustment several times
a season.

If your engine has a separate starter (seems like an 18 Hp might have
to, this starter/gen combo on my 12 Hp barely can turn the engine over)
then it id harder to know whether it still works. You can open it up
and examine for fried coils. A few years ago, Auto Zone could test
old-style generators, but I wonder if they still have the equipment.

Jon