Wiring diagram for a 77 RV125 is here:
viewtopic.php?f=29&t=4743
Your 1972 RV125 is likely somewhat different than shown in the 1977 wiring diagram.
I may have found a wiring diagram for an earlier RV125 in this tread on another forum:
http://www.2strokeworld.com/forum/index ... ic=20322.0
The diagram is:
The earlier diagram shows a different ignition switch & no voltage regulator.
It shows that a resistor is used as a substitute load when the lights are off.
Would seem reasonable that the early RV125 did not have a voltage regulator & the later models did.
Both wiring diagram show a mixed AC/DC design with a half-wave rectifier.
Some components run on DC & others run on AC.
The AC powered components are only powered when the engine is running.
The headlight runs on AC -- so you need to check it with the engine running.
The flat-bottom headlights are hard to find & are getting quite expensive.
Your bike probably doesn't have a voltage regulator.
So its worth considering using a cheap alternative headlight while you are making sure everything is good.