shouldn't be too hard to figure out. just start pulling spaghetti: check your ground wire, then start jiggling the blue/white and blue/red (from memory on my 72 - yours could be different) back from the headlight, into the handlebar switch, through the switch on the headlight case, etc. check the bullet connectors from the wiring harness going into the headlight case. there's many possible points of failure, you just have to find the right one(s).
The blue wire is the hot lead to your handlebar switch where it splits into either high or low beam power. If neither filiments works, check to see if the lead from the headlight switch in the shell is plugged onto the switch. Then see if you get power from either the blue/white (high) or blue/red (low). See if there is power coming from the ignition switch to the headlight switch. Sometimes, on the bikes with the ignition switch in the headlight ear, the wire works loose on the switch, or the rivet on the switch works loose.
Also, check the ground (red) wire for continuity from the bulb holder to the battery + terminal.
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