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LED Brake / Tail Light Conversion

Cruiser


Toadsucker’s LED Brake / Tail Light Conversion
for the Suzuki Intruder 1400

After having my tail light bulb burn out on me one dark night I started thinking about an LED conversion. First off, I’m no electronics wizard. However, a little web surfing found a schematic for an LED brake light at:

http://www.web-ee.com/Schematics/Brakes/brakes.htm

That circuit, and the information and electronics formulas presented with it, gave me a decent starting point. The circuit only acts as a brake light, though, and since I wanted the LED’s to function as both tail and brake lights, a trip to Radio Shack netted me some resistors of varying values to experiment with. Eventually, I modified the circuit a bit by adding a second resistor for tail lights, and lowering the resistance value used for the brake lights in the original circuit to provide a brighter light, while still maintaining a margin of safety by keeping the amperage below the 40 mA the LED’s are rated for. The difference in brightness is very noticeable.

I placed an order for 60 Ultrabright Red LED’s from DigiKey . My modified circuit uses strings of 5 LED’s in series. There are 6 strings wired with both the 330 ohm (tail light) and 100 ohm (brake light) resistors for tail and brake lights, and 6 wired for just tail lights with only the 330 Ohm resistors.

The circuit diagram I came up with is shown in Figure 1 (one of each 5 LED strings).

Parts List:

LED’s – Digi-Key part # 160-1034-ND [60 needed - $15.68 including shipping]

Resistors – Radio Shack part # 271-1315 (330 ohm, ¼ watt) [$0.99 pkg – 3 pkgs]

Radio Shack part # 271-1311 (100 ohm, ¼ watt) [$0.99 pkg – 2 pkgs]

Modification of the stock tail light begins by taking the assembly apart and discarding the unneeded parts, like the heat shield, bulb, and inner bits of the socket . You will have to very carefully cut the crimped end of the outer rubber boot to remove the wires. Save the small rubber grommet that the wires pass through, the rubber boot, and don’t remove the ground lead from the outside of the socket.

After taking a few measurements of the reflector, I designed a printed circuit board that would mount the 60 LED’s and required resistors. 30 LED’s are in three concentric circles. These LED’s act as both tail and brake lights. The remaining 30 LED’s are mounted in 6 arcs, 3 on either side, with 5 LED’s per arc. These are for tail lights only and do not function as brake lights. The design of the printed circuit board is shown full size in Figure 2 (positive image).

To create the PC board, I went to “U-Do-It Electronics” and purchased a printed circuit board kit (for positive images) manufactured by MG Chemicals. This kit (Catalog # 416-K, $34.95) contains pre-sensitized boards, chemicals, rubber gloves, brushes, and a plastic storage bin that doubles as a developing tray. MG Chemicals has instructions on their website, along with a video outlining the process. I used the 6” X 6” board supplied in the kit to make two circuit boards.

I used two 18” fluorescent bulb fixtures on a simple wooden stand to expose the boards, rather than spending additional money for their Exposure Kit. You can also make PC boards using a photo negative method, (see Figure 3 for negative image) but there are more steps involved and a special exposure light needed (you can use sunlight at noon, but this was a winter project, remember?) Whichever method you decide to use, and whatever kit you purchase to do it, READ and FOLLOW THE DIRECTIONS CAREFULLY, and OBSERVE ALL PRECAUTIONS! The etching chemical (ferric chloride) can be rather nasty to work with. Again, rather than purchase the MG Etching Kit, which was rather expensive, I purchased a cheap aquarium pump and hose from Wal-Mart for under $7.00 to aid in the etching process.

Figure 1
 
Figure 2
Figure 1
 
Figure 2
     
Figure 3
 
Figure 4
Figure 3
 
Figure 4

Once the board is etched, and all that remains is the copper pattern, you’ll have to drill the numerous holes in the solder pads, and cut and trim the outline. The two + marks on the outer tabs need to be drilled with a 21/64” bit. Now it’s time to solder jumpers and components to the board. I mounted all components (LED’s and resistors) on the side opposite the copper circuit, passing the component leads through the holes for soldering. Jumpers and feeds (20 gauge wire) are wired on the circuit side. Solder the 330 and 100 ohm resistors in as shown in Figure 4. Solder in wire leads for Brake Light +12V, Tail Light +12V (these leads should be a bit longer than the original wires and of the same gauge as original, or you can use the original wires if you cut them right at the socket), and Ground Lead (about 6 inches will do) where shown. Solder in jumper leads to connect like-marked holes (J1 to J1, T3 to T3, etc.) When soldering in the LED’s, mount the SHORT terminal (the anode [+] lead) towards the power feeds (T# and B#), and the LONG terminal (the cathode [-] lead) towards the ground circuit. Test each string of 5 LED’s as you solder them in by connecting your ground lead and your tail light and (if one of the center ring strings) your brake light +12V feed wires. If you goofed up, it’s a lot easier to unsolder and reverse one now.

With everything soldered in and working properly, carefully feed the brake and tail light power leads through the holes in the rubber grommet from the socket. You may want to tie a small knot or use a small wire tie around the wires to act as a strain relief. Drill a small hole into the side of the socket, strip a small (1/4”) bit of insulation from the end of the ground lead and feed the wire through the hole, soldering it to the OUTSIDE of the socket. Carefully slide the PC board (LED’s facing out) into the tail light assembly, guiding your wires through the opening in the rear of the socket. The 21/64” holes should slide over the screw towers. When the board is even with the top of the reflector, square it to the towers and apply a small amount of epoxy to hold it in place. I added some black silicone sealer around the wires and grommet, and around the cut portion of the original boot to seal out any moisture. Install your lens, and reinstall on the bike, making certain your wires are connected properly (ground to ground, brake wire to brake light +12V, tail light wire to tail light +12V). Double check to make sure everything works, then go riding!

This Tip Courtesy of Toadsucker From The Cafe

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It Is Your Problem.
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Get Help From Someone Who Is

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