yeah I don't think a headlight that flashes all the time is the best option, though I see them all the time so I assume it's legal (for bicycles not motorcycles), I want to be able to press a button to make the light start flashing, if a headlight suddenly goes from steady to flashing that should really help to get somebody's attention in an emergency situation, or just for fun and to show off to my friends

also I think I'll need to use a 5AH SLA Battery instead of 10 AA NiMH (max available 2.7 AH) or I could use 10 NiMH C cells which are also 5AH but more expensive

I need a 12 volt system because I also want to hook up a car horn.

here's another schematic http://www.diylive.net/index.php/200...light-flasher/
it doesn't use a relay, and no transistor, I have no idea what the transistor is for (I don't know a lot about electronics) but I like the design with a relay since I can see how it could work with a momentary button the way I want