83 Aero charging issue and headlight.

[Circusbear]

I had an issue with the 83 aero 50 not charging the battery. I was only getting 4 volts back to the battery and the battery would eventually die. After tracing the wiring, replacing the rectifier, replacing the stator I was still only getting 4 volts. Sat down with the wiring diagram again and found that someone had replaced the headlight with a modern halogen bulb, a Sylvania 9005. Removed the halogen bulb and PRESTO! I am getting 14 volts back to the battery. It was the $%&* bulb the entire time. I knew the headlight was very bright but this being my first scooter I assumed it was normal.

Now here is the question. What is the best bulb to replace this with?