Modify a AA mini-maglite to be a long-lasting, low-key CHEAP bike light. Features LEDs for long battery life and handlebar-mounted remote controls. You can even continue using the flashlight off the bike. Perfect for urban nocturnal stealth rides.

This instructable relies on an off-the-shelf AA minimag and LED module, brand name "NIGHT-IZE." It was about $12. It also relies on several serendipitous brackets and clips to mount this stuff to my bike. Readers can search out the exact stuff I used, but I figure the average Instructables reader is resourceful enough to figure out their own version.

Other materials/tools: miniature momentary and toggle switches, 10" lengths of 24 AWG wire, some heat shrink, a 1/8" female phone jack and plug. I used a TRS (stereo) plug but it doesn't have to be. In fact some other kind of jack/plug combination might work. Oh, and the spring from a retractable ballpoint pen!

The LED module is not terribly bright - about the same as a 3-LED head-worn lamp. Don't bother comparing it to some $150 HID paint-peeler. It is enough to to see the path in the woods or the crusties lurking under that bridge. My night-ride philosophophy is stealth. As someone else on this site said, "they can't aim for what they can't see." My system uses a momentary and a toggle switch in parrallel so I can have the light on all the time or only when I pull the trigger.

Step 1: Mod the Flashlight Tailcap

I'll let you follow the package directions to install the Night-Ize LED module. Our first step will be drilling out the aluminum tail cap of the minimag. Our goal is to install a female 1/8" audio jack (or whatever you found to use) in the tailcap. There is a bored-out hole already where the stock replacement bulb lives. Take that bulb out along with the plastic sleeve that protects it, and save them.

I don't know the threads on my jack, but I compared them to my tap and die set and decided 5/16-24 would be close enough. A pilot hole was drilled, enlarged to 17/64", and tapped.

Step 2: Assemble Modified Tailcap

A cone shaped spring comes with the flashlight to complete the circuit in the tailcap. Discard it. The basic idea is to replace it with the jack and a smaller spring (from a ballpoint pen) to make connection between the "tip" portion of the jack and the battery. A plastic sleeve (drinking straw piece) makes sure the pen spring doesn't short out against the alu body of the light, and directs it towards the battery contact. Trim the sleeve so that almost touches the battery base contact when the tailcap is spun on completely. The metal body of the jack grounds to the aluminum body of the tailcap, completing that side of the circuit.

Step 3: Control Surface

Since you now have remote access to your maglight though the 1/8" jack, you can use any combination of simple switches to control it. I used both a momentary and SPST toggle switch (wired in parallel) so I can choose to leave the light on or use it with discretion. To keep my options open for future expansion (tailight!) I ran a separate cable to each switch and joined them at the plug. Some creative heat-shrink and nylon abrasion shield braid makes it look slightly cooler. I also potted the switch connections with hot glue so the solder joints have less chance to be stressed by vibration.

The switches were mounted in a plastic clamp I scrounged off an exercise bike. You get to be creative in finding your own switch mounts.

Step 4: Mount It All to Your Bike

To mount the light I use a microphone clip, because I had one and its intended microphone (Sennheiser ME80 shotgun) matches the diameter of a mini-maglight well. It's snug and made of slightly flexible nylon, and adjusts for tilt. I'm sure if you don't have mic clips idly lying around, you can figure something else out. If you want to try a mic clip, a local music store might have something. Take the light with you to make sure it grips snugly. If it's loose the light will pop out over bumps.

The controls clamp to the handlebar. A little forethought and tricky cable routing with my ancient rapidfire shifters put the switches in a good ergonomic spot. In fact I figured out a kung-fu grip that allows me to shift, brake and blind those raccoons simultaneously.

Step 5: Ride!

That's it. Fine tune the position of the switches, fix any dodgy connections, and fly though the night. Just be safe, see them and don't let them see you.

Notes:

If you want to use the flashlight off the bike, you can: 1) replace the modded tailcap with a stock one, or 2) make up a dummy plug that is shorted out to make the light stay on. Even better, use a jack with an integral switch built in (analogous to when plugging headphones in makes the main speaker cut out on radios, etc.)

The LED module comes with a retrofit reflector that prevents focusing the light. It is permanently focused to about a 60 degree spot. Most of the light is about 6-10 ft in front of the bike, but it definitely will make reflective signs glow up to 200' ahead of you.

I have been using the same batteries for over 3 months (intermittent use, 4 nights/week, 3-4hrs per ride)