Alt. light flickering at high rpm???

Might be time to test alternator at parts store. An internal field short to rotor, and grounding by bearings, in may increase voltage output with flicker. That fits with greater voltage, light load too. The regulator could call for zero field, but short provides path. 1 wire alternators are hard to diagnose, when the field wiring is not where it can be monitored. It could also be badly internal regulator, but less likely. Who knows..... not many fix with small parts these days, they are even hard to get. Just swap it, some poor folk will get it back in a cheep rebuild, and pass it down the line.