Funny you mention it...
My older brother had a '78 185 Twinstar that was the 6-volt system. The battery died and he bought a 12-volt battery from WalMart just because it was the same physical size. He didn't even realize the original was a 6-volt!!
Naturally, it blew all the bulbs on the bike, but he never put two and two together. Then, it sat... and sat... and went through a move, then sat some more... He never really knew what the problem was, and eventually, he just gave the bike to me but never mentioned any of the details until much later.
I knew nothing about the bike (6-volt or 12 or anything), and I didn't pay attention to the cruddy, burned up bulbs when I took 'em out, so I just put on a junkyard 12-volt headlight and a new taillight bulb, blinker bulbs and dash bulbs - all 12 volt.
The bike ran like an absolute champ for the next 10,000 miles as my daily driver on a 60-mile-per-day commute with no other changes whatsoever! Headlight was very bright on my dark-in-the-morning commute, blinkers blinked fine, horn beeped, starter work fine, etc. It was MONTHS before I picked up some information that tipped me off that the bike was supposed to be a 6-volt system!!! This was 3 or 4 years ago, now.
So, for me, there were NO changes that were necessary other than the battery and the bulbs. But then, I had a pretty high-rpm commute, so I think the system was able to keep the battery charged just fine. If you ride mostly 'round town at lower rpms, you might have some problems...
Good luck,
Kirk
