That can be caused by (among other things) an internally corroded battery ground strap.Same effect if the black (ground) to the regulator has a problem.
A story; a now passed on forum member and a good guy had been fighting charging problems for a long time, threw lots of parts at the problem, to no avail. Finally convinced him to bring the bike to TSOIR. Another buddy was here with me when the bike got here. We had the problem isolated, repaired in 20 minutes flat.
Not that I'm a guru, just that electrical problems yield to methodical troubleshooting just like everything else.
It doesn't hurt to have KNOWN GOOD parts to substitute in, along with meters and jumper wires to isolate the issue.
PLEASE do not ruin another rotor (#3)