Cheap and unstealable bicycle taillight instructions

This is the first non-ecology/evolution post on this blog, but bike safety is another important subject in the world and one of very few that I feel qualified to write about publicly. Because you want every chance against the moron driver reading his/her cell phone and not paying attention to the road around his/her four-ton SUV, it is important to be visible. Reflectors are necessary, but having a taillight in addition is always a good idea.

(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...

Building a cheap taillight that isn't likely to get stolen is fairly easy - and as a bonus, this is brighter than most of the more expensive ones! Here's a quick run-through of the materials and how to do it. It took me less than 10 minutes, even while taking these photos.

Really all you need is a 9V battery terminal, 2 sections of red LED and ~6 inches of two colors of wire.

Materials (in two parts):

Things you already have:

Hot glue gun/glue
Soldering iron/solder
Electrical tape
Zip ties
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. 

Plug in your soldering iron and hot glue gun.

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. 

Time to do some really easy soldering. place your soldering iron on one side of the twisted together connection - wait for it to heat up and draw solder through the other side to get a good solid connection (see above).

LEDs with solder on the copper contact points.

Now get a drop of solder on the copper contacts on each LED (see picture above). Place the tip of your soldering iron on the copper and the tip of your solder a hair away also on the copper - let the copper heat up and draw the solder instead of melting the solder directly on the iron.

Solder drawn through the 3mm stripped ends. 

Then draw solder into the wires on each of the 4 on the 3 mm stripped end. Now look for + and - signs on the LED contacts and line up your wires. The soldering here is easy - without using any solder, press your presoldered wire onto the top of the little solder bubble on the correct contact. With a little pressure, the solder from the contact and the wire will melt together and you will get a good contact (see below).

Good connections to the LEDs. 

Now test your connections - gently tug them (don't PULL) and then put the battery in.

Good connections. Make sure not to cross your two soldered connections, as it looks like is occuring here (though it actually isn't). 

Cut off a little bit of e-tape and wrap each of the 2 to 1 wire connections. Use your hot glue gun and place a nice bead of glue over the just soldered LEDs - this will waterproof that connection (which would short with just a little water). Make sure the hot glue goes over any exposed wire or copper contact on the LEDs.

Waterproofed!

Now mount it up to the bike. This will depend on your set-up. I used zip-ties and super glue - I wasn't worried about ruining the paint on this older, cheaper, beat up bike. If you are, use double-sided tape or zip tie the LED strip on. The adhesive backing on the LEDs themselves are junk - you'll have to do something else. I mounted the 9V under the seat, where it is unobtrusive and less likely to get really wet.

Mounted and working! Note the battery zip tied to the seat rail. Make sure your seat is in good position if you do that. 

My back of the envelope calculations for battery life expect about 10 hours with a GOOD QUALITY 9V battery and the LED draw that was on the packaging (not sure whether that is correct). Don't buy batteries at the dollar store. Also note - most LED strips, including the one I used, run brightest at 12V (and are "rated" at 12V). On my other bike, I run the longer strips off a 6V battery (and have 2' of wire, which allows voltage drop) and red works fine, however, it won't run clear or green. Red is the least sensitive to low voltage and it draws the least (good for battery life!).

(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...

Late 1950's Huffy Daisy Daisy tandem, with green "ground effects". Currently powered off a 12V motorcycle battery (would probably last a year on it!), but I'll get a rechargable 12V pack for it eventually (still working out the kinks of the bike - it was in many boxes when I bought it a couple months ago).