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Solution to replacing lights on CB100

3390 Views 2 Replies 3 Participants Last post by  Tanshanomi
Hey all, new here. Just got myself a 72’ Honda CB100 with a CL100 engine swap. Im replacing the lighting and fenders, but I’m running into an issue with finding compatible lights. Everything that I’ve found that is low profile runs on 12v, but the bikes battery is only 6v. Haven’t done a TON of research just yet, but what are some of my options? Do I completely swap the system to 12v, assuming the wiring can handle 12v and nothing else on the bike runs off of the battery (I’m pretty sure nothing else on the bike needs battery power considering it’s a kick start)? Lemme know what you think and any links to products and resources would be much appreciated. Cheers!
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The electrical system on those OHC Honda singles is not very sophisticated. It is nominally a 6V system, but since it's unregulated, its actually sort of a "somewhere in the neighborhood of 6V most of the time" system. To convert to 12V, just replace the original crappy slenenium rectifier with a proper 3-wire 12V rectifier/regulator. Don't get one of the little cheapo ones, get a heavy-duty one with a sizeable heat sink on it. There are three AC wires from your lighting coils, but simply connect the white and yellow alternator wires together to one AC terminal. Unfortunately, there isn't space to mount the reg-rec in the same spot as the original rectifier, and there isn't very good airflow for cooling under the side cover anyway. I ended up mounting mine up front, under the headlight. (I eventually flipped it around so that the terminals were at the top, where the connections were a little more protected from the elements.)

A 12 volt conversion won't do anything about the alternator's wimpy amperage, however. As small and old as your alternator magnets are, you're lucky to get much more than 3–4 amps out of it. The good news is that by switching to 12 volt LED lights all around (including the headlight!) you can have nice, bright lights and still have enough current left over to keep the battery charged. You will, however, need to add a diode kit to the turn signal indicator circuit for the turn signals to work properly. Speaking of the battery, you'll have to switch to a 12V battery, of course. You'll have a tough time finding a 12 volt battery that fits in the space for the orignal 6V battery. I went with a much larger capacity AGM battery, but that required building a custom battery box:

The ignition system will run 12V just fine with the stock points and coil, though there are more robust 12V coils that are have the same mounting centers as the original and are marketed specifically for Honda 12 volt conversions.

To sum everything up, here's a custom wiring diagram I made up for my 12 volt CL125S:
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