Just thought I would share my recent experience. I was given a LT 3600 and told if you can get it to run, you can have it. So I cleaned the carburetor, spark plug, and air filter. Put in fresh gas and checked the oil, then proceeded to fire it up. Lo and behold it was not charging the battery. Having many years of experience working on small engines, the rectifier/regulator was the first suspect! I looked up the part number through a Yamaha dealer and found that the best price was about $119.00 usd. After a little research and a hunch I found out that the rectifier/regulator from a Yamaha LT3600M snow mobile will work just fine. Yes I installed it and it works! Better yet it only cost $13.80 usd through ebay.
Pn. LD1799154RV. It took a little 'adjusting' to make it fit, but no big deal. Wiring harness plugs right in as it should. All I had to do is to drill out the mounting holes a little. This mad me very happy, and I hope it helps anyone else with this problem.