Let there be light!
I have spent the last few days chasing down an electrical gremlin... For some reason, I was only getting 6 volts to the headlight low beam wire, and about .15 volts to the high beam wire. A little research on the internet indicated that headlight problems are often caused by a corroded starter switch or a corroded high-low switch. The starter switch has a headlight cutoff so that the starter motor can get maximum voltage when starting the bike. I took apart both of these switches. The hi-low switch was a bit crusty, but didn't look too bad. The starter switch had cocoons or spiderwebs growing inside of it.
After scraping these out, the headlight still didn't work. I was pretty frustrated, but I took a wiring diagram and started tracing the headlight circuit. As it turns out, the problem was not in the switches. It was the fuse. This totally eluded me because I was getting SOME current through the circuit. Using the wiring diagram, I started unplugging harnesses and testing the headlight circuit from the headlight back to the power source. There was a voltage drop before the starter switch and before the headlight switch, so I knew that those were not the cause of the problem. The wire straight from the fuse box was also putting out about 5.6 volts. I opened the fuse box again (it was the first thing I checked), saw no breaks, and pulled out the fuse. Here's what I found:
The fuse had broken in the end cap. It hadn't blown; it had simply snapped. This allowed a small amount of contact, which closed the circuit, but didn't provide enough of a current path to power the light. Anyway, I have a headlight that works, and as a bonus, two sets of smoothly operating switches!