# Making custom tail lights with led's ( Another one)

#### solidshark91493

Joined May 2, 2017
8
Hi everyone. Decently long time lurker. New member. I know there are endless posts like this and I have searched before I post. Ive been researching this the past couple days and Ive seen its a possibly not allowed topic? Im not too sure so let me know if Im not square. I also apologize for the massive wall of text Im about to unleash. But Im here to learn!

I have a 1990 Toyota supra and I want to make a custom set of LED tail lights for it. I have attached an image of what Im trying to emulate. The guy that makes them wont even discuss how he made them with me even though he's trying to get rid of the last sets he has as he doesnt want to make them anymore. I dont plan on selling them. Ever. I just dont have 800 bucks to blow on a set of pre made lights when Id rather do it myself.
Looks like per light, There are:
Red:30x8
White(Reverse only): 8x3 x3 rows
Amber Turn signals: 15x3 x 3 rows

Im a novice with electrical and I know a bit how things work, I was planning on going with Red, Amber, and white superflux led's with these specs:
Red:
Forward Voltage: 1.8 ~ 2.2V
Luminous Intensity: 4000 ~ 5000MCD

Peak Wave Length(nm): 620 ~ 625
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA

White:

Forward Voltage: 3.0 ~ 3.4V
View Angle: 100 ~ 120 degrees
Color Temperature: 6000 ~ 7000K
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA

Amber:
Forward Voltage: 1.8 ~ 2.2V
View Angle: 100 ~ 120 degrees
Peak Wave Length(nm): 585 ~ 590
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V

I know series is a no no but thats about as far as I know how to go until I get some input. I havent messed with circuitry for so long I need a long refresh course on the basics. So I dont want to do any short cuts and I want to make the best quality setup I can.

So with that said... Lay it on me!

#### mcgyvr

Joined Oct 15, 2009
5,394
You are in trouble.. Its "parallel" thats a no-no.. Series is fine..
And specifically its parallel without each having its own resistor..

All you need to do is create multiple series circuits (each with its own resistor) and put a bunch of those in parallel..

So.. I'll just show how one would be done and hopefully you can take it from there..
Red LED..
The max Vf=2.2V..
Assume you have 12V to work with.. (typical nominal car batter voltage.. it could be higher too.. up to like 14.3v but I would just use 12v as the starting point)
12/2.2 = 5.45
Round down that means you can have 5 LEDs in series
Then you simply need to size the resistor for that series string..
Shoot for 20mA through each string..
So to size the resistor its resistance = (Vs - Vf)/I where Vs = source voltage, Vf=forward voltage of all the leds in the string and I = current
So (12-(5x2.2) = 11 then 11/.020 =50 ohms and the best "standard" resistance value is 56 ohms (there is a chart of standard resistor values I used)
So you need a 56 ohm resistor..
and its 11V because the forward voltage of each adds up but the current stays the same in the string so thats why its still 20mA and not 20x5mA

Now you need to figure out the minumum wattage that resistor needs to be
Well that formula is I^2*R where I = current and R = resistance
So .020^2 * 56 = 0.0224 watts.. Then you multiply that number times 2 or 3 for a "safety factor"..
So you want a minimum .0672 w resistor.. So just use a 1/8W resistor as they are very standard..

So now we have determined everything we need for your red LED circuit..
And thats
240 LEDs..
We said 5 max per string
So thats 240/5 = 48 series strings in parallel each with its own 56 ohm 1/8W resistor..

and now to show you how easy it is to calculate the rest..
Use this..
http://led.linear1.org/led.wiz
Enter the following values
Source voltage = 12
diode forward voltage = 2.2
diode forward current = 20
number of LEDs = 240
and check the "schematic" radio button and click "design my array"
and voila..
It matches exactly what I just calculated..

Now see if you can do the rest on your own..

Read my post over and over till you understand the formulas and you are "golden" and should be lighting up the night in no time..

Now.. If you find that 20mA is just to bright (and it can be) then you can choose 10mA instead of 20 or whatever.. and adjust the resistor for that..

Have fun.. I hope you like to solder.. Thats a crap load of wiring to do..

#### mcgyvr

Joined Oct 15, 2009
5,394
@solidshark91493 Just "shouting" you out so you know a reply has been posted.. Not sure if it sends an email or whatever..

#### MrAl

Joined Jun 17, 2014
9,516
Hi,

It's hard to tell from your description but you have to be a little careful that you dont modify the car too much or it might not pass inspection. Not sure if they will notice either, if there is a serious modification.
If it is just LED's it's probably ok though. The lens would show that it was modified if the lens itself was altered.

#### drc_567

Joined Dec 29, 2008
1,156
It is likely that the tail light circuit is detected by a Light Failure Sensor. This component will turn on a warning light in the instrument panel if insufficient current flow is detected ... It thinks that a tail light is out. One solution is to install a shunt resistor, in parallel, across the LED panel to increase the current.

#### ian field

Joined Oct 27, 2012
6,536
Hi everyone. Decently long time lurker. New member. I know there are endless posts like this and I have searched before I post. Ive been researching this the past couple days and Ive seen its a possibly not allowed topic? Im not too sure so let me know if Im not square. I also apologize for the massive wall of text Im about to unleash. But Im here to learn!

I have a 1990 Toyota supra and I want to make a custom set of LED tail lights for it. I have attached an image of what Im trying to emulate. The guy that makes them wont even discuss how he made them with me even though he's trying to get rid of the last sets he has as he doesnt want to make them anymore. I dont plan on selling them. Ever. I just dont have 800 bucks to blow on a set of pre made lights when Id rather do it myself.
Looks like per light, There are:
Red:30x8
White(Reverse only): 8x3 x3 rows
Amber Turn signals: 15x3 x 3 rows

Im a novice with electrical and I know a bit how things work, I was planning on going with Red, Amber, and white superflux led's with these specs:
Red:
Forward Voltage: 1.8 ~ 2.2V
Luminous Intensity: 4000 ~ 5000MCD

Peak Wave Length(nm): 620 ~ 625
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA

White:

Forward Voltage: 3.0 ~ 3.4V
View Angle: 100 ~ 120 degrees
Color Temperature: 6000 ~ 7000K
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA

Amber:
Forward Voltage: 1.8 ~ 2.2V
View Angle: 100 ~ 120 degrees
Peak Wave Length(nm): 585 ~ 590
Reverse Current (uA) : <=30
Viewing Angle : 120 ~ 140 Degree
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V

I know series is a no no but thats about as far as I know how to go until I get some input. I havent messed with circuitry for so long I need a long refresh course on the basics. So I dont want to do any short cuts and I want to make the best quality setup I can.

So with that said... Lay it on me!

Pretty sure Elektor magazine covered this a couple of years ago - their website is easy to find and you can probably order photocopy or reprint of the original article.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
Intensity can change with Vf, so you might want to sort the LEDs by Vf You can then modify the series resistance. The color of the LED changes perception too. Amber in daylight MIGHT be more sensitive to intensity.

You have a lot of LEDS and you would like them to be the same intensity, so you can likely bin them based on Vf and use different resistors for different ranges of Vf.

If you'd like the LEDS to work at 8V say which might happen when the car is disabled and the battery runs down. so the LED sting sum of Vf should not exceed the intended operating voltage. The resistor or a constant current source drops the rest of the voltage.

For cooling you may want to use an aluminum circuit board. http://www.mclpcb.com/products-and-services/aluminum-pcb No affiliation. Never used company.

I have a couple of lamps that are designed around this https://people.xiph.org/~xiphmont/thinkpad/PT4115E.pdf IC. There are 10 pairs of LEDs. Each pair has a 100 ohm resistor in series and it will operate at 6V to 24 V at full brightness.

e.g. 2.4+2.4 is less than 6 and some voltage is dropped across the 100 ohm resistors well. They are white LEDs.

It almost looks like a flexible PCB glued/laminated onto a 0.062" sheet of aluminum. That's your heat sink. The LEDS are surface mount.

I want to try dimming, but it's not that easy to modify.

See: https://www.maximintegrated.com/en/app-notes/index.mvp/id/3070

EDIT: Easier to understand and application note

Last edited:

#### solidshark91493

Joined May 2, 2017
8
Alright, Home from work! I appreciate all the replies. Im gonna go through and read them all and edit/comment again when Im finished.

#### solidshark91493

Joined May 2, 2017
8
You are in trouble.. Its "parallel" thats a no-no.. Series is fine..
And specifically its parallel without each having its own resistor..

All you need to do is create multiple series circuits (each with its own resistor) and put a bunch of those in parallel..

So.. I'll just show how one would be done and hopefully you can take it from there..
Red LED..
The max Vf=2.2V..
Assume you have 12V to work with.. (typical nominal car batter voltage.. it could be higher too.. up to like 14.3v but I would just use 12v as the starting point)
12/2.2 = 5.45
Round down that means you can have 5 LEDs in series
Then you simply need to size the resistor for that series string..
Shoot for 20mA through each string..
So to size the resistor its resistance = (Vs - Vf)/I where Vs = source voltage, Vf=forward voltage of all the leds in the string and I = current
So (12-(5x2.2) = 11 then 11/.020 =50 ohms and the best "standard" resistance value is 56 ohms (there is a chart of standard resistor values I used)
So you need a 56 ohm resistor..
and its 11V because the forward voltage of each adds up but the current stays the same in the string so thats why its still 20mA and not 20x5mA

Now you need to figure out the minumum wattage that resistor needs to be
Well that formula is I^2*R where I = current and R = resistance
So .020^2 * 56 = 0.0224 watts.. Then you multiply that number times 2 or 3 for a "safety factor"..
So you want a minimum .0672 w resistor.. So just use a 1/8W resistor as they are very standard..

So now we have determined everything we need for your red LED circuit..
And thats
240 LEDs..
We said 5 max per string
So thats 240/5 = 48 series strings in parallel each with its own 56 ohm 1/8W resistor..

and now to show you how easy it is to calculate the rest..
Use this..
http://led.linear1.org/led.wiz
Enter the following values
Source voltage = 12
diode forward voltage = 2.2
diode forward current = 20
number of LEDs = 240
and check the "schematic" radio button and click "design my array"
and voila..
It matches exactly what I just calculated..

Now see if you can do the rest on your own..

Read my post over and over till you understand the formulas and you are "golden" and should be lighting up the night in no time..

Now.. If you find that 20mA is just to bright (and it can be) then you can choose 10mA instead of 20 or whatever.. and adjust the resistor for that..

Have fun.. I hope you like to solder.. Thats a crap load of wiring to do..
I love to solder.. but im not very good at it and I need a new soldering station and a good way to learn how to solder properly and keep the life of my tools up. I have a soldering station I got on amazon thats a chinese brand and the heat gun never worked and the soldering iron quit shortly after I first tried it (Too late to warranty apparently.. )
Gonna try to figure out using that formula/link what I need for the other two and get back to you. Maybe try to make a schematic.. never tried it before.

Hi,
It's hard to tell from your description but you have to be a little careful that you dont modify the car too much or it might not pass inspection. Not sure if they will notice either, if there is a serious modification.
If it is just LED's it's probably ok though. The lens would show that it was modified if the lens itself was altered.
Im only swapping out the insides, I live in Nevada and It just has to be visible at 500 feet day or night I believe. Only real requirement besides colors which are obvious.

It is likely that the tail light circuit is detected by a Light Failure Sensor. This component will turn on a warning light in the instrument panel if insufficient current flow is detected ... It thinks that a tail light is out. One solution is to install a shunt resistor, in parallel, across the LED panel to increase the current.
In my research I do recall hearing something about this.. I thought it was in the Mk4 supras.. but Ill try looking into it and Ill also look up info on those resistors

Pretty sure Elektor magazine covered this a couple of years ago - their website is easy to find and you can probably order photocopy or reprint of the original article.
Did a quick google search and didnt quite see what I was looking for.. I didnt want to sign up there.

Intensity can change with Vf, so you might want to sort the LEDs by Vf You can then modify the series resistance. The color of the LED changes perception too. Amber in daylight MIGHT be more sensitive to intensity.

You have a lot of LEDS and you would like them to be the same intensity, so you can likely bin them based on Vf and use different resistors for different ranges of Vf.

If you'd like the LEDS to work at 8V say which might happen when the car is disabled and the battery runs down. so the LED sting sum of Vf should not exceed the intended operating voltage. The resistor or a constant current source drops the rest of the voltage.

For cooling you may want to use an aluminum circuit board. http://www.mclpcb.com/products-and-services/aluminum-pcb No affiliation. Never used company.

I have a couple of lamps that are designed around this https://people.xiph.org/~xiphmont/thinkpad/PT4115E.pdf IC. There are 10 pairs of LEDs. Each pair has a 100 ohm resistor in series and it will operate at 6V to 24 V at full brightness.

e.g. 2.4+2.4 is less than 6 and some voltage is dropped across the 100 ohm resistors well. They are white LEDs.

It almost looks like a flexible PCB glued/laminated onto a 0.062" sheet of aluminum. That's your heat sink. The LEDS are surface mount.

I want to try dimming, but it's not that easy to modify.

See: https://www.maximintegrated.com/en/app-notes/index.mvp/id/3070

EDIT: Easier to understand and application note
Those boards look great. Heat is a concern I hadnt addressed yet. Unfortunately I have bad experience with SMD component led's xD
Last time I used those was the PSP modding days.. I burned so many of those suckers from getting stuck to my soldering iron haha.

As far as the operating voltage, I guess Ill have to mock a couple of each color on a perfboard and see how bright they are at 500ft and go from there. Im not sure if Im getting that part correct.. ? Im a little confused.
I need to figure out how to do the brightness and dimming of the brake lights and the turn signal blinking.. Not sure if I need to change anything on the signals..

Lastly, Any good reading material on components, how they work, and general electrical diy stuff? I really want to start over with the basics on the side of this project. I want to understand how the stuff works not just put it together

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
Last time I used those was the PSP modding days.. I burned so many of those suckers from getting stuck to my soldering iron haha.
I can see how it would happen for the inexperienced. You need lots of hands.

The solder you use has a lot to do with it as well as the technique. Leaded 63/37 works OK for surface mount stuff, but you would want a paste. If you get a PCB made, you would usually get a stencil to apply the paste.

At least with paste, it's paste or stencil, place, ( hold and heat) which is a two-hand operation. With SMT it might be easier to get rid of the heat.

63/37 lead solder is unique because it solidifies instantly. 60/40 would act like glue and stick to the iron.

There is a couple of low temperature alloys I like. Sn96 is a common high temperature lead free I don't particularly like.

You can also glue the components down, a Superglue kind of stuff that will release when you twist the component.

I missed the "parking/brake light" thing.

In an Impala, I made most of the interior lamps LED's. They were #194 incandescent. All work fine. The car has dimming and turns the lamps off when they are on too long,so you can't accidentally leave your interior lamps on.

This works for the trunk lamp too. That one is a higher intensity and larger #194 variant and needs a different pattern. That one isn't working quite right. If you just open the trunk, it will stay on in a dim mode for a very short time and turn off. If you open a car door, it will brighten and stay on the proper amount of time.

I recently tested a 75 ohm resistor in parallel and it worked. No lamp burn out stuff. So, I have to add it.

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#### SgtWookie

Joined Jul 17, 2007
22,227
Taillights are really not a good project for a novice.

Think about this for a few minutes. The taillights are the only warning that someone following you will get, that you are going to turn, slow down, stop, etc. And then consider that person following you is going a bit fast on a state highway. And one of those not-so-great solder joints you made on a made-in-China bargain basement LED decides to fail, right when it's needed most.

Safety items like this really should wait until you have a lot more experience.

The life you save may be yours.

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#### #12

Joined Nov 30, 2010
18,223
I was chasing down a, "no tail lights" problem in a Chevy today and found properly fitting LED bulbs at three auto parts stores.
A bit pricey at $24 per pair, but that seems cheaper than 10 or 20 hours designing and building a pair that might, or might not, pass inspection or be reliable. Thread Starter #### solidshark91493 Joined May 2, 2017 8 Taillights are really not a good project for a novice. Think about this for a few minutes. The taillights are the only warning that someone following you will get, that you are going to turn, slow down, stop, etc. And then consider that person flowing you is going a bit fast on a state highway. And one of those not-so-great solder joints you made on a made-in-China bargain basement LED decides to fail, right when it's needed most. Safety items like this really should wait until you have a lot more experience. The life you save may be yours. Ha, I knew from my research through the forum Id see you sometime. Im going to use a spare set of tail light housings. I generally dont plan on using these unless Im going to a car event or something of the like and I wont use them unless they are bomb proof. Besides, even if my solder on china led's fails there will be 200 plus of them so It wont matter much plus I plan to do a lot of testing before mounting it. Also might swing by the ol police station and have them check them out and make sure they are safe before they go out on the road. Dont get me wrong I see your point and its very valid. I just plan to be extremely thorough if I do this project and it wont go on the road until Im 110% sure it will keep me and others safe. And if Im not 110% sure it wouldnt leave a parking lot with them installed. #### MrAl Joined Jun 17, 2014 9,516 I love to solder.. but im not very good at it and I need a new soldering station and a good way to learn how to solder properly and keep the life of my tools up. I have a soldering station I got on amazon thats a chinese brand and the heat gun never worked and the soldering iron quit shortly after I first tried it (Too late to warranty apparently.. ) Gonna try to figure out using that formula/link what I need for the other two and get back to you. Maybe try to make a schematic.. never tried it before. Im only swapping out the insides, I live in Nevada and It just has to be visible at 500 feet day or night I believe. Only real requirement besides colors which are obvious. In my research I do recall hearing something about this.. I thought it was in the Mk4 supras.. but Ill try looking into it and Ill also look up info on those resistors Did a quick google search and didnt quite see what I was looking for.. I didnt want to sign up there. Those boards look great. Heat is a concern I hadnt addressed yet. Unfortunately I have bad experience with SMD component led's xD Last time I used those was the PSP modding days.. I burned so many of those suckers from getting stuck to my soldering iron haha. As far as the operating voltage, I guess Ill have to mock a couple of each color on a perfboard and see how bright they are at 500ft and go from there. Im not sure if Im getting that part correct.. ? Im a little confused. I need to figure out how to do the brightness and dimming of the brake lights and the turn signal blinking.. Not sure if I need to change anything on the signals.. Lastly, Any good reading material on components, how they work, and general electrical diy stuff? I really want to start over with the basics on the side of this project. I want to understand how the stuff works not just put it together Hi, Check your soldering iron element and your heat gun element. Those are the things that burn out sometimes. You can get a new iron for maybe 5 dollars USD which will plug right into your station, but make sure you get the right type with the right connector. For the heat gun you'll probably have to find a new element. Yeah, instead of red LED s install green LED's That would confuse the heck out of the driver behind you: "Do i stop now or go?" How about a nice shade of blue? ha ha. This would also be funny if a driverless car got it's color recognition system mixed up and saw green instead of red. Thread Starter #### solidshark91493 Joined May 2, 2017 8 Hi, Check your soldering iron element and your heat gun element. Those are the things that burn out sometimes. You can get a new iron for maybe 5 dollars USD which will plug right into your station, but make sure you get the right type with the right connector. For the heat gun you'll probably have to find a new element. Yeah, instead of red LED s install green LED's That would confuse the heck out of the driver behind you: "Do i stop now or go?" How about a nice shade of blue? ha ha. This would also be funny if a driverless car got it's color recognition system mixed up and saw green instead of red. yeah Im pretty sure its toast. Ill keep it and try to fix it eventually. #### KeepItSimpleStupid Joined Mar 4, 2014 5,088 I posted it in the wrong forum. Head's starting to get messed up (migraine starting). Sorry. Thread Starter #### solidshark91493 Joined May 2, 2017 8 All good #### ian field Joined Oct 27, 2012 6,536 I was chasing down a, "no tail lights" problem in a Chevy today and found properly fitting LED bulbs at three auto parts stores. A bit pricey at$24 per pair, but that seems cheaper than 10 or 20 hours designing and building a pair that might, or might not, pass inspection or be reliable.
The price has more to do with how long they last - the dealers have to make a living somehow.