Hustler Z not charging

I have a Hustler Z 60" deck 24hp Honda. 1700 hrs Mowed for the first time last week and everything went good. This week I mowed all the front and went to the back. Engine started to sputter then died. Would just click after that. Jumped it and headed back to the house. I kicked on the PTO and mowed 2 strips and sputtered and died like before. Jumped it. Checked the battery with my meter. Full throttle about 12.4 v. Unplugged my coil leads and got 36.67 vac and about 14.06 amps. This is the 20 amp charging system. I know the amps are a little low but I'm thinking it's a bad 20 amp rectifier/ regulator. I would like to know for sure before spending $100 on a new rectifier/ regulator. Thanks