Cheap and Easy LED 3rd Brake Light Conversion! (NA, and maybe NB?)

[jnshk]

I've kind of been wanting to upgrade my CHMBL (aka 3rd brake light) to LED, but hadn't been impressed by most of the usual options.

- I was not impressed by any of the 921 LED bulb replacements available. The reflector design lends itself to lopsided/directional lighting if using a non-incandescent bulb.
- The off-the-shelf options currently available seemed ridiculously priced considering how inexpensive the components used to make them are.
- I thought about building my own LED array on a panel or circuit board, but decided that it wasn't worth my time, effort, and the cost of gathering up all the needed supplies.

Then I had another idea; all I really needed to do was find a small universal LED strip that would be suitable as a brake light and also small enough to fit into the housing. After trolling through the Grote and Trucklite catalogs and all the cheap (though sometimes expensive) crap from China on eBay and Amazon, I began to get discouraged. Luckily, I stumbled upon a promising candidate at Summit Racing: http://www.summitracing.com/parts/upd-39687b/overview/

The part arrived today and I am happy to report that it's just about perfect for retrofitting the NA (and probably the NB?) 3rd brake light! The strip is a 3-wire design with a dim (taillight) and bright (stoplight) setting. The dim setting is probably on par with the stock 921 bulb, the bright setting is substantially brighter. It fits easily inside the housing, and in fact you could probably stack two of them in there if you wanted to get really crazy. Two lights would definitely be overkill though, and might be a potential safety hazard if wired up to use the bright setting. It would definitely look cleaner and be easier to keep things more secure (because you could tape or glue one strip on top of the other, and then tape the top and bottom to the lens) with two of them though. I keep thinking that it would be cool to make a "version 2.0" with two strips and wire up a limit switch on the brake pedal so that it uses the dim setting on normal braking and then steps up to the bright setting on hard braking. I really like that idea, but it also seems like more work than I care to do at the moment.

I played with a handful of ways to mount the strip inside the housing, and ultimately decided that 1/8" to 3/16" from the bottom and mounted parallel to the lens yielded the cleanest view when illuminated. When centered vertically, most of the light appears to come from the top half of the lens because of the refractive lens and the angle from which it is usually viewed (looking slightly downward). When mounted toward the bottom half of the housing, it illuminates the lens quite evenly from most angles.

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I used a couple of rubber bumpers to space it from the bottom of the light, and to keep it in place I glued it with some clear silicone adhesive and a couple dabs of super-weatherstrip adhesive on the lower corners. Then I drilled a couple of holes and put two screws in to help secure it even more. Looking back in hindsight, I should have just used some thick 3m double-sided tape. It would have been way quicker, easier, and cleaner.

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I might pick up some 194 bulb wiring adapters (like these (http://www.ebay.com/itm/4x-T10-W5W-194-168-Adapter-Led-SMD-Panel-Stop-light-Marker-LICENSE-PLATE-Female/161002883643) found on ebay) so that I can plug it directly into the stock harness and keep it very tidy.

I've attached some pics of the light and how I mounted it, but no "action shots" yet as I'm waiting for the glue to cure before I put it on the car.



TLDR?
1. Buy this light http://www.summitracing.com/parts/upd-39687b/overview/
2. Tape, glue, or screw it to inside of stock 3rd brake light housing
3. Hook up the red (+) and white (-) wires
4. Reassemble and reinstall
5. Laugh at all the suckers who pay $40-$80 for LED 3rd brake lights

[Agent☣Orange]

Wow! Thanks for the great write up!

[iKhanh]

good idea man. you should post pictures of it in your car working and stuff, to give an idea of the light output.

[atank]

Good write up and less than $10 bucks..............

[SM16RMSM]

Pictures of it in action?

[Phatmiata]

good idea man. you should post pictures of it in your car working and stuff, to give an idea of the light output.

would like to see that as well, great write up btw, Thanks Given!

[jnshk]

Reassembled and installed the new light today, so I snapped some pics for you.

STOCK (Day)
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LED (Day)
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LED (Night)
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The pictures probably don't do it justice. In the day the difference is only noticeable if you are intimately familiar with Miatas, but at night it's very obvious that the third brake light is more intense than the regular brake lights. I feel like the result is pretty good as it is right now, but I am really itching to make version 2.0 with two LED strips... :D

[Agent☣Orange]

Whoa! Couldn't miss that at night.

[jnshk]

Started work on version 2.0 tonight. It's looking very promising!

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Notes:
- You can't just slap them in the front like you would with a single LED strip, because the combined size is big enough to prevent the lens from seating properly.
- This is actually a good thing, because if you could fit them under the lens, the top strip would be firing mostly into the weatherstripping gasket around the lens.
- By moving the LED strips back, you can take advantage of some of the reflector housing. This in turn produces a much more even light from all angles, and also gets rid of the shadowed effects when not illuminated.
- Is it bright? Yeah, it's pretty bright.
- It's definitely a lot more work than a version 1.0 conversion, but not too difficult and still a great project for under $20.

Once I'm sure everything is the way I want it, I will probably seal it all up and mount it on the car so that I can get some pics for you guys.

[jnshk]

Updates!

Version 1 ------------------------- Version 2 Low ---------------------- Version 2 High
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Version 2.0 is awesome! While the intensity of Version 1.0 hi and Version 2.0 hi could probably only be detected if viewed side-by-side or back-to-back, the "fill" of the light is most definitely improved. As you can see in the Version 2.0 lo image, instead of the thin visible strip of light seen in Version 1.0, the light completely and evenly fills the lens. Similarly, on the high setting the light is dispersed evenly and fully across the lens.

I haven't decided if I will use the low setting or the high setting yet, but for the moment I am going to run it on high (for better daytime visibility). I suppose that if I wanted to get fancy I could wire up a relay to use the low setting when the headlights are on (night time) and the high setting when they are off (daytime), but for now I'm going to K.I.S.S..

Tomorrow or Sunday I will try to snap some daytime pics, as well as do a more detailed write-up on the process for building a version 2.0.

UPDATE: Version 2.0 day time pics.
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On the low setting, it's probably on par with stock. On the high setting, it looks washed out in the photo but it's actually a deeper red than the regular brake lights in person.

[jnshk]

OK, here's a basic "how-to" for version 2.0.

1. Remove the red lens cover, and remove the metal heat-shields from the reflector housing.
2. Use a dremel, jigsaw, or hacksaw to cut along the line where the mounting area crosses the bottom side of the reflector housing. Cut up the sides, but DO NOT cut the top off.
3. Mark off the depth of the LED strip when placed at the first cut, and then make your second cut across the bottom of the reflector and up the sides, parallel to the first cut.
4. Join the two cuts and remove the section of reflector from the housing.
5. Using a dremel or file, clean up the edges of the cuts and make any additional clearance necessary so that the LED strips can be slipped into the newly cut out area. **Tip: I left this as a tight fit so that the back of the reflector housing would press against the LED strips and help hold them in position.**
6. Grind or file down the tab grooves on the top of the reflector that held the heat shield in place. This will allow you to push the LED strips all the way up against the reflector housing.
7. Using the dremel tool or file, grind down the little lip that is left over on the bottom of the reflector housing. This will help let the bottom row of LEDs shine wider and clearer.
8. Feed the wires through the back of the housing and position your LED strips in the cut out so that they are centered and tight together in the housing.
9. Mark and drill small holes (1/8") in the mounting area of the housing. One on each side (left and right) directly above and one each directly below the mounting holes for the LED strips.
10. Use 4" zip ties to secure the two LED strips together, and then again to secure the top strip to the top of the mounting area and the bottom strip to the bottom of the mounting area.

If possible, now is a good time to test everything out and make sure it all works as expected. If it's all good, proceed.

11. Use some clear Silicone RTV Adhesive (I prefer the Permatex brand) to run a bead along the edges of the cutout to seal the lamp housing. I also squeezed out some globs around the mounting tabs of the LED strips and the zip ties in order to keep it all secure.
12. Put it somewhere that is well ventilated and let it cure for a couple of days.
13. Mount the assembly in the car and hook up the wires with whatever method you prefer (plug-n-play bulb adapter, wire nut, solder, crimp connector, etc.). Red=Hi(+), Black=Lo(+), White=Ground(-)