Small Engines (Lawn Mowers, etc.): Lawn Tractor Chraging System Help, poor connections, charging systems

Question
I have a 12hp B%26S in my lawn tractor and I can't seem to figure out why it's not charging the battery.

It starts with a boost and runs great but when you shut it off it won't start again.
So I went out and got a new battery and it does the same thing.

From what I was told the three wires that are on the engine one black wire by it's self is the wire for the shut off. (Is that right?)
The other two wires one red and the other black. The red goes to the battery side of the solenoid for the charging system and the black wire gets grounded to the frame.
If that's the right way for it to be wired what else could be wrong with it??

Any info would be great.

Thanks
Andrew

Answer
Here is a good link on charging systems/alternators:
http://www4.briggsandstratton.com/miscpdfs/RNT/alternator_replacement.pdf

This link will help identify the alternator wires:
http://www4.briggsandstratton.com/miscpdfs/RNT/alternator_id_a.pdf

The link below covers charging system testing:
http://engines.myfaqcenter.com/Answer.aspx?p_faqid=3438&body_0$tbKeyword=alterna...

Do you have an electric PTO clutch?  Briggs alternators are pretty reliable but I have found a couple of bad diodes.  Having said that, most defective diodes were caused by connecting the battery backwards, reversed polarity.

One item often over looked is clean connections.   I have fixed a lot of charging problems just by dis-connecting the battery and cleaning the battery post and cable ends with a wirebrush.  Even through there is no visible corrision, poor connections can cause all kinds of issues.

Let me know if the links help and about the electric PTO.

Eric