Crazy electrics on my tea20

Looking for some guidance if anyone can make sense out of what is happening as detailed below:

Having sorted a LOT of minor problems with my new Fergie, Im kind of stumped with this scenario..
I was told when I got the tractor that is had a short somewhere and drained the battery. I have since discovered that this is true and that the alternator isn't charging unless I fiddle. The alternator is an unknown. I have no idea what make/model as someone spray painted it grey. It has a regulator mounted to it on the outside underneath, not the back.

I worked out that the igntion light was stuffed. When I fitted a small 12v test light instead, it lights up with the key on, start the engine, it goes out and the alternator charges around 13.6 ish.
Then I started to get a different scenario. You could turn on the key, no light! And then the alternator wouldn't charge but when you turned it off, it wouldn't stop the engine unless I broke the test light connection.

Puzzled, I reconnected the light, turned on the key. And the first scenario came back. Light on, light goes out, charge, turn key, engine stops!

Anyone got any ideas on what gremlins are lurking? I figure the drain is possibly a stuffed diode in the alternator?

I had to start using another multimeter when my first went flat but gave up as the tractor sends the display haywire, especially when you connect the positive the battery (with no negative connection, and worse when both are)

Looking forward to your thoughts.

Cheers
Chris

I suspect you are correct in thinking you have diode problems, perhaps a loose solder
connection. Now you get to contact your local alternator rebuild shop and inquire as to
the exact item you have and a possible correct wiring hook up. It is possible to wire in
most any alternator from Delco to Mitsubishi and several in between. Not to mention the
option of painting it most any color you desire.

I had same problem before, turn key off and motor would keep running, the exciter wire for alt was feeding into the ignition circuit. bad alternator.

The randomness leads me to think you may have crusty points in the regulator. I'd start with cleaning them, just in case it's an easy fix. Does happen sometimes you know....