(EDIT/UPDATE, 12/2016 - I switched from using the cheaper lights shown in the pictures here - to using 5050 lights, which are a quite a bit brighter. I think the added brightness is worth it, and they aren't much more expensive. I don't know what it does to battery life. - I've also switched from hot glue to heat shrink tubing, but hot glue is still cheaper and more people have a hot glue gun than a heat gun)
In Davis, and likely elsewhere, head- and taillights are stolen constantly and decent ones are expensive (>$20). I suspect those two reasons are why so many folks in Davis don't have taillights (don't get me started on helmets!).
|A cheap - ~ $2 taillight. Brighter than many on the market, weatherproof, long-lasting...|
|Really all you need is a 9V battery terminal, 2 sections of red LED and ~6 inches of two colors of wire.|
Things you already have:
Hot glue gun/glue
Wire (I used 22 gauge)
Things you may need to buy:
9V battery terminal (2.99 for 5 at RadioShack, WAY cheaper online in bulk - free if you take it out of some old piece of electronics!)
Red outdoor LED strip lights (this is the kicker - its about $10 for 5 meters - you'll need about 4" - but useful for all sorts of projects or you could make ~90 sets of tail lights).
|The Royce Union's seat stays. Note already flaking paint - not going to screw anything up here.|
Next, place your battery terminal under the seat, the LEDs where you want them, and cut 4 pieces of wire to reach between the two. then strip each wire - on one side strip about 3mm and the other about 8 mm. Strip the ends of the battery wires about 8 mm if they need it, too.
Now cut a section of LED at the cut points (noted on the strip, on mine, these are every 3 lights). Cut the terminals out of the plastic on the LEDs.
Decide which color wire is going to be hot (+) and ground (-). This is important in LEDs unlike normal light bulbs. Twist the two hot wires (8mm stripped end) together with the red wire leading from the terminal. Do the same with the black wire and other two.
|Soldered connections. Yellow is my "hot" wire, blue my ground.|
|LEDs with solder on the copper contact points.|
|Solder drawn through the 3mm stripped ends.|
|Good connections to the LEDs.|
|Good connections. Make sure not to cross your two soldered connections, as it looks like is occuring here (though it actually isn't).|
|Mounted and working! Note the battery zip tied to the seat rail. Make sure your seat is in good position if you do that.|
(UPDATE: that same battery is going strong 11 months later. I commute on this bike often, though I didn't for about 5 months of the field season. I don't know how many hours I have over the 11 months, but I'll bet its well over 10!).
Now you can use the rest of the LED strip for other projects...