On my 111 lawn tractor I upgraded from a 11hp to a 12hp I/C engine. The old 11hp had one wire coming out of the charging system going to the wire harness. The 12hp I/C engine has 2 wires both with 13v outyput when running. I have one hooked up to where the original 11hp wire went, but it doesn't seem to charge enough beacause th battery will be dead after a mowing. Should this other wire be connected too, or should it be run to the pto to spare the load on the charging system? I'm not ruling out a junk battery here yet either. Basically what I'm wondering is, can this 2nd wire help with charing in some way.

I can't give you a complete answer, but here's a little info that may help. Briggs uses different stators for the electrical output requirement, 3 amp, 10amp, etc. If the equipment the replacement engine came from did not have an electric clutch to support, chances are the stator does not supply enough amperage to keep up with the load, thus an extra draw on the battery.
Some of the two wire stators have one wire with a diode built in to one of them to provide DC voltage for the battery, the other is actually still AC for running headlights. My only experience with a single cylinder Briggs using an electric clutch, had a larger rectifier mounted externally to the engine. Don't know what the stator capacity was for that one, but it would have to be 10amps or more. The smaller clutches, in good condition, will pull around 4 amps, so a 3 amp system would not keep up the battery while mowing.
If you have a service manual for the tractor, it may show some details about the charging system. You may be able to switch the stator/electrical setup from the original engine and solve the problem. Another tip-check out the local library for a Briggs and Stratten engine manual. You will find info for all their charging systems and how to identify them.
Hope this helps a little.

tommyhawk

Odds are the two wires are from an AC coil under the flywheel. A rectifier/regulator will be required to convert the AC to DC and limit the voltage to about 13.8V.
Test across the wires and from each wire to block with an ohmmeter and tell us what you have.