i'd test the stator output.....set meter to AC volts....find the 3 yellow stator output wires (unplug the rr, they will be accessible from the harness fitting)
test 1 to 2, 2 to 3 and 1 to 3, writing down readings of each, which should be near 60 AC volts with engine running at 4,000 rpm. Any variations to above readings... stator no good. If they are all equal and near 60...RR may be bad. I happen to have a plug-in MOSFET RR which fits both the 250 pregen and EX500
https://faq.ninja250.org/wiki/How_do...system_work%3F