Make your Mercedes more visible at night - LED taillight DIY - PeachParts Mercedes-Benz Forum

tbomachines · #1 11-27-2010, 09:43 PM

A common criticism of driving an old mercedes (particularly a diesel with a cloud of black smoke behind) is the lack of visibility at night. I can always pick out a w123 or w126 from a distance because of the dimly lit, downward-facing running lights. Stepping on the brakes does not do too much either, unless you are blessed with a third center brake light. With that in mind, I realized that there was a large portion of the w126s taillights that are NOT being used at any given time. There is the inside red lens where the euro fog lights would go (but U.S. versions have nothing) as well as only half of the main red area being used for running lights. Since I have a spare w126 laying in the yard, I took one of the tails off of it to experiment and this writeup is a result of that experimenting. I have a working prototype and will be converting the other taillight as soon as I can run down to the parts store for another LED light. Advantages of this LED light setup:

Using the ENTIRE tail light area as running lights, therefore increased visibility--meaning running lights are angled towards other drivers and not just the ground as stock is set up
brighter and truer red color
much quicker response time compared to normal bulbs
using the typically blank euro fog lights for additional brake lights - increased visibility
LEDs last much longer and usually do not have to be replaced as long as they are not subject to varying current
Its really easy

Disclaimer: I am not responsible for any harm or damage as a result of your following these directions. I am not implying or expressing that these taillights may be street legal in your local area.

Ok, so here is what you need:

- figures 1.1, 1.2: a DOT-approved 3 prong LED taillamp from NAPA, the type that you see on trailers and trucks. Cost about $25 if I remember correctly. Mine was about 3.5" diameter, filling up the whole red area of the tail light
- w126 tail lamp assembly
- soldering iron plus flux, shrink wrap, solder, and bullet-type electrical pins
- some way to cut plastic. Doesn't need to be pretty. I used a dremel with a variety of tips
- super glue
- about 1-2 hours of time

1. Completely disassemble the tail lamp. You'll have to separate the gasket (good time to replace it too), lens assembly, "reflector" assembly, and the metal strip with light sockets.

2. cut out room for the LED lamp in the reflector assembly. This takes some time and patience to get perfectly right. I got it after about an hour of trimming. You have to make sure to take the middle light separator out. Interesting note is that the plastic is crudely painted "reflective" silver. I can't imagine it doing much good in terms of light reflectivity.

3. Eventually get the LED snug in the reflector assembly so that it presses up against the lens/refractors (figures 3.1, 3.2). A couple dabs of super glue to the reflector assembly will make sure it doesn't go anywhere. Secure the screws to the lens, making it all one piece again. A good idea to test out the LED on a car battery for proof of concept (figure 3.3)

4. Wiring! Everybody's favorite thing! Actually it couldn't get ANY easier than this. First off, take either the bulb socket for the running lamp or the taillight and snip the wire off of it. Put that bulb socket in the "blank" space, where the euro fog light would go. The LED bulb I had already had the appropriate connections molded into the plastic: "tail", "ground" and "brake".

Connect and solder:

black and red wire to the "brake" connector. Solder this to a bullet type connector and plug in. Solder in another wire to the bullet connector (so it will have two coming off of it) and solder the other end to the socket you just popped in the euro fog spot. Having these two in series will trick the car into thinking there is no bulb out (LED resistance is negligible in comparison) and they will light in unison.

Connect the Green/white wire to the "tail" plug via another bullet-type connector

Solder the ground wire/bullet anywhere on the metal strip holding the bulb sockets. The whole thing is a ground.

After that is all neatly done you can connect everything back up (figure 4.1)

5. Plug it in and try it out! (Figure 5.1) See the difference--I apologize my camera is NOT good at taking night shots so it is difficult to see. The camera actually makes it look a bit worse than stock but I can guarantee you in person the difference is dramatic. Remember that LEDs produce one wavelength of light and bulbs produce a spectrum, I think that whatever the wavelength is for these LEDs is not well reproduced by my cheap camera whereas the spectrum is sort of a "flood" of light. Anyways, I noticed the normal taillights are not only pointing down and using 1/4 or so of the available space, but they are also amber colored. Using the LEDs brought light to the entire surface including the part FACING drivers behind you, and they light brighter as the brakes are hit. The biggest difference is the added brake light. Originally I used a larger bulb in the socket but it was too bright (figure 5.2). Putting a smaller bulb (like that used in the old running light socket) was perfect.

I will feel much more comfortable cruising around at night in my 300SD now knowing that people behind me will actually know I am there now, and know when I am braking. The addition of a center brake lamp will also compliment the enhanced visibility of this project, that is certainly on the list for me. I hope you guys find this useful!

Figures:
1.1, 1.2: The LED lamp that I used. Typical truck lamp.

Figure 3.1, 3.2: The aftermath of a lot of cutting/trimming

Figure 3.3: proof of concept hooked up to car battery

Figure 4.1: wired and ready for assembly

Figure 5.1 brakes on:

5.2: with the "euro" bulb that was too bright

tobybul · #2 11-27-2010, 10:36 PM

In case you don't want to do the LED, installing a 2nd 1157 brake bulb in the empty compartment will do just as good of a job. Everything is there. All you need is the bulb and IIRC a jumper wire to connect it.

I believe I posted this some time back like 3-4 yrs ago.

Otherwise, they sell 1157 LED bulbs too but I don't know if they fit or howell they work.

tbomachines · #3 11-28-2010, 01:43 AM

Quote:

Originally Posted by tobybul

In case you don't want to do the LED, installing a 2nd 1157 brake bulb in the empty compartment will do just as good of a job. Everything is there. All you need is the bulb and IIRC a jumper wire to connect it.

I believe I posted this some time back like 3-4 yrs ago.

Otherwise, they sell 1157 LED bulbs too but I don't know if they fit or howell they work.

I will have to look for your writeup - the only ones I saw were for using it as a fog lamp (same general idea, but more wiring up to front). I also toyed with a dual filament bulb so it would serve as both running light and brake light. I wouldn't mess with the drop in LEDs for taillights, their pattern is not the same. I'd stick to the DOT approved trailer lights since they fit and have a good beam pattern

mike-81-240d · #4 11-28-2010, 02:07 AM

I don't think this size fits in the w123.

micalk · #5 11-28-2010, 10:37 AM

What affect do the LED lamps have on Cruise Control operation? Theoretically, since you are including the original bulb in the setup, the control unit would still see the application of the brakes as a removal of ground. Without it, you might see problems as I think the LED might not provide the conductive path that the bulb provides when not operating.

tbomachines · #6 11-28-2010, 02:56 PM

Quote:

Originally Posted by micalk

What affect do the LED lamps have on Cruise Control operation? Theoretically, since you are including the original bulb in the setup, the control unit would still see the application of the brakes as a removal of ground. Without it, you might see problems as I think the LED might not provide the conductive path that the bulb provides when not operating.

Honestly I'm not sure because my car is not registered yet (just finished swapping an engine in) and theres no telling if the cruise even works. However since the brake bulb is installed in series with the LED, it should be no problem. The car thinks that the only thing there is the one bulb since the LEDs draw such little current they are virtually invisible on the way the old circuit is designed. That's why if you just throw in a LED in place of a regular bulb you'll get your bulb indicator on the dash.

tbomachines · #7 11-28-2010, 02:57 PM

Quote:

Originally Posted by mike-81-240d

I don't think this size fits in the w123.

The procedure is probably the same though, I can't imagine the two are that much different. Might have to settle for a square LED tail cluster or something but really its a matter of cutting out the reflector to fit the LED.