2008 crf230l electrical charging issue

[kens]

Soooo I have a 2008 Honda crf230l motorcycle that the charging system works perfect IF the head lamp is disconnected and charges at 13.5 at the battery. If the headlamp is connected the dc output at the battery cannot exceed 12.3 volt...... been such a small battery it eventually leads to a battery that won’t start the bike.
ohm test of the stator seems good, ac output from all 3 legs of the stator are equal and within proper voltage, I did substitute a new bulb in place and no change, ground from headlamp plug is good.

I googled all day looking for any knowing issues and found nothing of note.

Any ideas of what is the cause? I’m leaning towards the regulator but definitely looking for information.