Instructables
In this instructable, you will learn how to prep an LED to be ready to install into a car! This means adding a resistor and soldering on some leads. When you are finished, you can do so many things with them and save a few bux too.



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Step 2: Solder the resistor

For this step, you will solder the resistor to the longer LED lead, or the anode. This is the positive. The resistor is needed to ensure that the LED only gets 2.5 volts and 20 ma from your cars electrical system.

You will want to trim down the LED and resistors leg so that you don't have a large area of flimsy solder terminals.

When you are finished soldering, slide some shrink tube over the resistor to prevent a short.

Step 3: Solder on some leads

Picture of Solder on some leads
Solder on some wire. Make it as long as you want. Use a 18 to 24 gauge wire.

Make sure that you use shrink tube to cover these connections as well. This is also very important.

Also, make sure that you have some indication of positive and negative. I used blue as positive (its all I had on hand) and brown as negative.

Step 4: Install!

Picture of Install!
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Drill some 5mm holes in your car where you would like to mount your LED and run the wires to a switched power source.

Some cars have a switched cigarette socket. In some cars (my case) i borrowed the switched wire from behind the radio. The radio turns off when you shut off the car and the LEDs do the same. If you want to be professional, you could find a blank fuse area and tie in. I opted not to do this...
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SOAD923 years ago
I was trying to do this but I have no idea on how to hook up it to give the LEDs power. Although I did do a simple circuit with a switch, but it was no big deal, and the connections I made to the 12v lighter jack would not hold to the little clips(soldered). If you can help me out on this I would GREATLY appreciate this!
SWV17876 years ago
My best friend did a similar install but hid a few green LEDs in his air vents it made a nice eerie glow when turned on.
computerwiz_222 (author)  SWV17876 years ago
IM DOIN THAT lol that sounds great! I would put white in my car because I have blue all over the floor, and white in my radio
green is good for holloween decor so is orange
Moomooco16 years ago
Can the resistor be more ohms than it needs to be? My led calls for a 390 ohm resistor when i don't have one!
computerwiz_222 (author)  Moomooco16 years ago
You can use a resistor that is higher, just not lower. Use the lowest resistance you have, and if it is not bring enough, you will need to get the proper one. If it is within a couple hundred ohms, you should be ok.
you can also put in more than one resistor.if u have two 50's they would equal about the same as a 100 or put in enough wire to add up to the correct resistance
Ok! thanks!
pdlbooboo5 years ago
i have a cig jack and i'm trying to put some leds in parallel but as i add more leds the further out ones get dimmer. how can i get around this. also i am putting a resistor on each led and am only trying to use 5 leds
computerwiz_222 (author)  pdlbooboo5 years ago
hmmm - well this sounds like you are using a long piece of wire (maybe 6 feet?) and the resistance is adding up causing the LEDs further down the line to get less current. You may want to consider using a heavier gauge wire The other option is to adjust your resistors. If there is 50 ohms of resistance in the wire up to the LED, subtract that from your resistor value (if you calculated a 560 ohm resistor, then you could get 510 ohms) LEDs have a brightness vs. current graph that is almost exponential, so even a 1 mA drop in current makes a huge difference (especially in the lower currents less than 20 mA)
there is no wire going in between each led. they r soldered directly to each other. i tried doing the same process accept with only one resistor on the first led. this worked ok but i don't know if this would shorten the life of the led or not. i dont know if i made this clear or not but theleds as a whole r not getting dimmer but instead it kinda goes like this.
LED.bmp
skip some of the resistors
nice, but i was wondering if its possible to wire it up to the interior overhead light wires, and put it up in the headliner, so it only comes on when a door is opened....and maybe in otherplaces as well, but ONLY when the door opens
computerwiz_222 (author)  Vic Rattlehead5 years ago
Absolutely! You simply have to source the wires coming from the dome light. It will only work when the dome light switch is activated or the doors are open.
i could wire them to my head lights for clearance lights on my motorhome.which in my state have no regulation on them.
could i possibly take out the main overhead light and use the wire ends from there? all i have for an interior is a single bench seat and no more room, so bright leds will be enough......
krazy27274 years ago
if you are doing a string of about 20, does each LED need a resistor on it?
krazy27274 years ago
if you are doing a string of about 20, does each LED need a resistor on it?
acer3595 years ago
did you connect all the LEDs to the same power source? Where did you get your LEDs?And one more more how would I make one blink?
ronnie945 years ago
Hi guys. For many times, I installed blue led in my car door handles using 560 ohms. After 3 or 4 days, all my blue led were busted. I tried a lot of times by connecting my resistors to th negative or positive or using 1 k but to no avail. What could have gone wrong?
computerwiz_222 (author)  ronnie945 years ago
What are the specs on your LEDs? If may have a lower voltage drop which would need a higher resistor value. Also, your alternator may be putting out a higher voltage (over 14 volts) which would also require a higher value resistor
According to the salesgirl, the value of the blue led is 1.5 ohm and she recommended resistor 1k. After a week all leds burned out. I tried resistor 560 ohms 1/2 watt or 1/4 watt but they all burned out. I tried 1.5k at 1/2 watt but the same thing happened. So I gave up.I tried yellow or green led at 1k and up to now they are perfect. But i prefer the blue light. What should I do?
Hawkeye90095 years ago
I know this is really old, but how could you build a dimmer switch for these?
computerwiz_222 (author)  Hawkeye90095 years ago
You can't really build a dimmer switch for these because they use such a small amount of current. You can build one using a potentiometer but 90% of the rotation will have the LEDs off - you need to use PWM (pulse width modulation) to dim LEDs properly and for this, you need a microcontroller or a circuit similar to the "atari punk console"
scientus6 years ago
This is a short and sweet instructable. I'm thinking of using this to convert an in-car light bulb for the dome light into one that has a few LEDs instead :)
Good idea, I already did it. Use 4 then you won't even need a resistor as the voltage divides across all 4 to give perfect amount to each LED. Plus you get to make your light any colour you want now! Mine are blue.
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gwolff antennas5 years ago
they would need to be wired parallel then, correct? or in series?
Rob K antennas5 years ago
Nice cup holder.
excellent instructable!!!
Brianjohn166 years ago
great job, but if i want to install them into my car, how do i wire them to power?
computerwiz_222 (author)  Brianjohn166 years ago
I simply tap into the switched 12 volts behind my stereo. This way the lights are only on when the car is running. I'm sure that there are better ways, but this seemed simple enough to me.
did you use resistors or just the right amount of leds so the voltage matched
computerwiz_222 (author)  Brianjohn166 years ago
Well there are two ways: 1 - just the right number of LEDs (not recommended) 2 - A higher wattage resistor and many LEDs in parallel. This method works when you need only one or two leds, but when you are mounting 50 like I did, it helps to buy prefabricated LED strips. They are around 20 dollars and have 20 or 25 leds in them. They are about a foot long. This method is great for under cup holders, ash trays or in the "trash bins" on the door panels of cars. If you want to see some pics of my finished rig, I would gladly show the finished product and the strips I am talking about.
Not sure why you don't recommend using the right amount of LED's it works great. LED's are current operated and will only draw what they need to operate. If you over drive the voltage it will still work but you shorten it's life since the junction doesn't like it and eventually fails. If you really over do it the junctions just blows and no more LED.
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In the second last block of text, I was referring to the way shown in the video.
i can turn on m stereo without the key......what about that?
you can also use switches. Put them in the "blank panels" that come in most cars.
gsmaur6 years ago
Cool! which LEDs are you using? there are bunch of with different light intensity (300mcd - 26000mcd).
teatimest6 years ago
Nice instructable! Does the resistor have to be on the + side? Does the resistor itself have orientation (color bands)?
computerwiz_222 (author)  teatimest6 years ago
The resistor can go on either side. Also, the resistor is not "oriented". We call this non polarized. An example of something that is polarized would be an electrolytic capacitor. The LED is polarized too. This means that it has a positive and a negative side.
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