Monday, December 12, 2011

LED Tail Lights

How to build your own LED (round tail) tail lights for around $100!

Preface: There are a few things you need to know before starting this project, if they are an issue for you, don’t do this!

1. Light output- Yes these are really bright, but no they do not look as bright as the original bulbs when compared side by side. The reason for this is the way the light gets spread around in the tail light bezels. With the stock tail lights, they use regular bulbs and the brightness of the bulbs is directly affected by how shiny the surround they are in is. By bouncing the light around in the housing, it gives the appearance of being pretty bright! However, LED’s do not use this concept. LED’s have a set degree (angle) of light output which is determined by the size and type of LED bulb, and can vary anywhere from 20*-360*. For this reason, they generally do not light up surrounding areas inside the tail light housing like the standard bulbs do, and it can make them seem less bright.

2. Time it takes to build these – Believe it or not, it takes and extremely long time to make these by hand. I timed how long it took me to build my final tail light assembly, from the time I pulled the stock tail light off the car, to the time the led’s were built and re-installed and working inside the car. It took approx. 14 hours solid of work, for all of the lights in the one tail light, and that was after I developed the most efficient way to put them together, and didn’t have mistakes or issues to go back and fix. It will eat up a weekend and then some making these… so be aware!

3. Cost- Although it cost me more than $100 to develop get these the way I wanted them, if you buy wisely, you can build them for about $100 or less. It is easy to spend way more than that if you go crazy and buy super expensive led’s, and buy all your resisters from radio shack etc. This write up also assumes you already have a specific arrangement of tools. If you do not have a tool listed, and cannot borrow one, you’ll need to consider that cost as well. I will give the sources I used to purchase my materials along with the prices of everything so you can see what you’re getting into before you start.

If you are ok with all of the above then you are ready to start building!


You are going to need to set aside a work bench, table, or something solid to do this work on, you are going to have a lot of little things flying around that you will need to be able to keep up. Also be sure your lighting is good. It’s really frustrating to work on this stuff with poor lighting (I bought this little $7 fluorescent light at Wal-Mart for this reason).


You are going to find you have a lot of stuff that is going to need to have a place to live while you’re working on this project. I found these little plastic drawers at Wal-Mart for $2 (MADE IN US!) they are great for storing little bits and pieces of stuff like this. I also have some file cabinet space for all my wires, big tools, and oem style wire connectors.


I have gathered a list of parts and supplies that you will need for this project, I recommend getting all of them before starting this, so you will have less lag time waiting for things to arrive or having to stop what you’re doing and running to town.


144 Red 5mm Superflux LED’s (for tail and brake lights) ~$40 (200 pieces)
32 Red or yellow 5mm Superflux LED’s (for turn signals) ~$15 (50 pieces)
78 White 5mm Superflux LED’s (for reverse lights, trunk lights) ~ $20 (100 pieces)

I purchased my LED’s from Niktronix of eBay, superfast FREE shipping, he’s based in the USA, and they have great customer support. You can get 100 of the same type of leds for half the price ($10 instead of $20), but they ship from CHINA and take several weeks, and lets face it if I can support someone in the US instead of China ill pay more!. I recommend getting the 5mm “Piranha” Superflux dome type leds. They are the brightest leds for your bucks (and the best suited for this type of application). Anything much brighter would need more complex boards made for them. I recommend getting more than you need, just because shit happens…


The cheapest thing you will need is resistors for your tail lights. We are going to need:

46 220 Ohm ¼watt resisters w/ 5% tolerance – for brake, tail, turn, trunk lights (>$5 on eBay)
18 68 Ohm ¼ watt resisters w/ 5% tolerance – for reverse light (>$3 on eBay)

You can buy these resisters at your local radio shack, but with the quantity you need, it will cost way more than getting them on eBay. At Radio shack they are $1.09 per 5 resisters…that’s a lot of cash. Get them on eBay, they will be much much cheaper and just as good.

220 Ohm Resister link (BE SURE TO GET 220Ohm NOT 220K Ohm)

68 Ohm Resister link (BE SURE TO GET 68Ohm NOT 68K Ohm)



RadioShack brand .022” Silver bearing rosin core solder ($6.99)
This one roll will be WAY more than enough, I’ve barely used half of it and I’ve made a ton of stuff!

I'm lucky and happen to have a drill press on my desk for this very reason, if you don’t not have a drill press, this will be a bit of a faff. I'm not sure what size the drill I used was, but you’ll only need to drill them a tiny bit larger. 

LEDs sit flush now 


After drilling the holes, I chose to paint the boards with some “chrome” paint to make them look more professional, but you don’t have to. DO NOT USE ALUMINUM TAPE ON THESE BOARDS INSTEAD OF PAINTING! I tried using this because it was so reflective, but it messes up the current flow and the leds WILL NOT WORK.

In this picture we are looking at the side of a red LED. On the left side is the thin anode (+) and on the right is the thicker cathode (-). MEMORIZE THIS! It is crucial to getting them put in the right spot on your boards. Touch the corresponding sides to the 3V battery and it should light up.

On other styles of LED’s, they usually will have one leg longer than the other, the long leg is usually negative. 


Now that you’ve tested all the leds for this board, we can put them on knowing that they will all work if we do everything correctly. Now we can put the leds where they are going to stay. These leds have four legs on them; we will only be using two of them (one + leg and one – leg). This helps make things half as complicated when we are connecting everything. The reason there are four legs is so they can be used on high vibration applications where they need the extra strength, but it doesn’t affect the light output or longevity. I found the easiest way to set the up on the board was to make the positive leg face the inside (closest to the turn signal) of the board like so.

I just cut the extra legs off with side cutters

We are doing 9 rows of 4, each row independent of the other. Be sure to put all the leds in with the same orientation as shown above. The pattern of the legs should be + - + - + - + - , with the positive starting on the inside, negative ending on the outside of the board.

On the back side we will push the first positive to the side, and then push the legs down, so that each positive is attached to the negative next to it. Leave the last negative to the side as well.

The back should now look like this

and the front of your board will look like this! 


Now that you have all of the positives and negatives where they need to be, now you can solder them together. Make sure the legs are pushed all the way through before doing this! Also – the legs of the LEDs are sensitive to the heat from the soldering iron, try it keep it touching the leds for as short a time as you can, it will roast your led if you heat it up too much (never had this happen, but they say if you leave the iron on it for 5+ seconds, it will kill it). In order to solder them together, all you need to do is roll out some of your silver bearing solder, lay it on top of the two legs you are soldering together, touch your iron on both the solder and the legs, and watch it flow and connect the two. Leave the legs on the ends alone for now.

Once you’ve done that, you should have something that looks like this> 

Next you'll need to gather up 9 of your 220 Ohm resisters (THIS IS FOR RED LEDS IN ROWS OF 4 ONLY). They are the ones that have the following stripe pattern – red red brown gold(may not be gold if yours have a different tolerance)
If you did not use the same led pattern I did (don’t have rows of four) you can figure out what resisters you need by going here.
Look at the specs for the leds you bought and fill it out accordingly.

Where you put the resisters is up to you, but you need to consider a few things first.
• The resisters cannot be touching any other connections.
• You must position the legs in a way in which you can attach a wire, again without touching anything else

The way I have this layout set up is so you have plenty of room on the outside portion of the board for your resisters. You will need to have one leg of the resister connected to the negative led leg you have left on the outside of the board. With this PCB board, you will need to leave 3 holes between each leg of the resister for it to fit properly. Tuck the resisters leg under the legs leg so you can keep track of where it needs to be.

I usually leave the remaining leg sticking straight up, it is the leg you will be soldering the wire to. Solder your legs to the negative led legs after trimming them to the appropriate length.
Should look something like this now 

Now that half of the resister is soldered to the led it will be a little easier to work with. Bend the remaining leg down and place it somewhere that will not contact anything on the board and trim to about ¼ inch. This is the leg you will be soldering your wires to. I used the small gauge RadioShack wires for this. Cut 9 pieces of wire about 2-3 inches long, and strip a small bit on one end to connect it to the resister.

Now “tin” your wires to prepare them for soldering to the resisters. Put your tinned wire on the board next your resister leg, with the wire facing the middle of the board (this will make it easier to fit in the tail light bucket). Solder them together! Check all connections to assure they are soldered together properly and will not come loose! Should look like this when you’re done

Next I go ahead and hot glue this section of wires since they can move easily. Let it dry completely before you move on to the next step.

Next you are going to bundle these together, cut them to an equal length, and strip the other ends of these wires in a way that you can twist them together in pairs of three (see pic)

I know it looks ghetto, but next you are going to solder them together into to one solid wire. Get your handy dandy pull apart OE bmw wires and choose which wire color you want to use, I chose brown with white dashes.

 Cut these 3 wires to be about 8 inches each, so you’ll have plenty to work with when you pull it through the tail light. Solder them to your wire bundles.

Again, pull on and bend the connection to make sure it is solid. Now slide a small piece of your 11/64’s heat shrink over the part you soldered, and shrink it!


We are going to follow the same process above to hook up wires to the positive legs. On this side, however, we will not need resisters. Simply cut your small gauge wires, strip them, solder them to the positive legs on the leds, join them together, and solder your 3 long wires ( I used blue with white dashes) to those bundles and your good!


This is possibly the most fun step. Take your two long wires, strip the ends of all three wires, twist them together and clamp on to them with your test leads. If you hook them up backwards you won’t hurt anything, they just won’t light up. In this picture the brown is -

Hook the other end of your test leads to a 12V battery and watch your board light up!

Exciting isn’t it? All that hard work paid off!


Now that all the wiring is done, you can either use hot glue or 5-minute epoxy to seal up all your connections and to ensure everything stays where it should. Hot glue is much better to use for this, because if you have an issue you can melt it and fix your problem, and it’s easier to apply.

Once that has cooled, I used my 10mm heat shrink tubing on the base of the long wires so that they are protected when you come up through the tail light hole.

Now a sharp eye will notice that I have removed the original tabs that used to push on the bulbs. The reason for this is because I don’t want that tab rubbing against my wires that are running through there, and I have no interest in using these buckets for OE bulbs again anyways. You can keep them if you want.


I'm not going to go into detail on the process for the remaining light, because you do the exact same thing. You will use your 220 Ohm resisters for the brake, turn, tail and trunk lights, one resister per row of 4 leds (or one row of three for the trunk light). You will use the 68 Ohm resisters for the reverse lights, one for each row of 4. I'm attaching all the picture I have from building the remaining boards below, and will comment if there is something you need to watch out for.

At this point you may notice that your white leds do not have the same type of anodes and cathodes inside them. Looking from the side this is what you’ll see

So how can I tell which on is positive and which is negative? Look on the bottom of the LED

The left side is smaller, positive, and the right side is wider, negative. Be sure to double check all connections before hooking them up the legs to each other, it is really easy to mix them up.


At this point, there are several directions you can go. You can attach spade connector to your wires and plug them right up to your OE wiring harness, or you can ditch all the crappy spade connectors like I did, and replace them with a modern style (5) wire connector. You can grab these all day at your local pull-a-part. I found some that have 5 wires going in, 5 wires going out, giving me the number I need! I used one 5 wire connector for the positive wires, and one five wire connector for the ground wires. 

Regardless of which you decide to do, you will need to cut the wires that are running out of the back of the tail light bucket to be the same length. After doing that determine which is positive and negative. I did this by striping the wires, twisting the like colors together from each board, and using the test leads to determine which ones which. I then tied a zip tie to the negative on all of them so I didn’t get confused

I then soldered the each like colored bundle of 3 wires together, neatly connected them to a wire coming off of the 5 wire plug. It doesn’t matter which on connects where at this point.

Once in the car you can choose how you want to connect them to the original wires, I soldered them all. Here’s how it looks before I tucked it away.

A follower of this blog submitted his own version of this 2002 upgrade on e21 rear lights....

Source - If you have any questions or comment, please post below or email me @
Zac Cardinal
1972 2002tii's Blog
1976 2002 "Margie"s blog

Source - 2002 FAQ,com_forum/Itemid,50/page,viewtopic/t,365899/



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