Your complete engine manual is available as a digital download from Kawasaki if you live in the USA.
AC goes from + to - but DC goes from + to 0
Thus you need 24v AC in order to get 12v DC.
There are 4 connections to a rectifier.
In your case 3 wires and a ground connection.
Because of the way they are made, bridge rectifiers usually have the connections opposite each other so you get DC- AC - DC - AC.
You can test the AC output to ground, each wire should show 1/2 what it shows between them