Acid was leaking from top of battery on my 75. I checked voltage around 3000 RPM and it was 16V. It looks like voltage regulator is bad. I will check wires, connectors and if they are fine I will try to install regulator from 84(I have it in my shed). It is not going to be easy because 84 has regulator with rectifier together as one piece and 75 has them separately.
Another idea is to feed headlight from wires going to regulator, it will drop current in one of alternator 3 wires( that is how I think regulator on 75 works.)
If your regulator is a point style, then just open it up and adjust it to your set min/max volt. I was having problems when I got my 74 CB550 and cleaned the regulator and reset the min/max voltage and now good as gold.