View Full Version : How to wire LEDs

01-12-2013, 06:04 PM
This will show you how to wire some LEDs to light add some light to your rig. Two bright red LEDs are going to be wired to a plug that you can connect to your receiver to power them up.

The plan is to end up with a servo plug going to a length of wire to an LED, then another length of wire to the other LED. These could be installed as a pair of brake or tail lights, or use white LEDs and you could have head lights.

For some, this is very basic stuff. For others, I hope this helps answer some questions and encourages you to build your own set of lights!


An overall view of the materials to be used.
Side cutters, needle nose pliers and wire strippers.
Two lengths of stranded wire (I think it is 22 gauge) that I recycled from an old network cable.
Two LEDs
Two 150 ohm resistors
Some heat shrink
A servo cable cut from an old servo


The LEDs need a resistor to limit the current flow or you risk burning them out or limiting their life. The two resistors shown here are 150 ohm (colour code: Black, Green, Brown, Gold). I will describe how I came to choose this resistance value in another post.
LEDs are polarity sensitive devices. This means they will only pass current flow in one direction. The LEDs have a few ways of telling you the polarity of their leads. There will be one lead shorter than the other, and that one is negative. Often there will be a flattened area near the leads and that also indicates the negative lead. I have clipped the negative lead of the upper LED and one end of each resistor.


Here you can see that the upper LED has been soldered to one of the resistors. To do this, I first tinned the areas I want to solder and then held them together and added a little heat until the tinned bits flowed together.
If you are wondering if these parts are heat sensitive, the answer is yes. The resistors can tolerate the heat well, but be quick on the LED. A good idea is to hold the LEDs lead with needle nose pliers right close to the LED body. This will help keep the heat from passing into the LED.


Both LEDs with a resistor soldered to their negative leads. The resistor is bent out like that to stop it from rolling over before I took the photo.


Prepping the wire for soldering... I've decided that the grey will be negative and the brown will be positive. The wire length has been cut and the insulation has been stripped to match the components to be soldered. Again, tin the wires before soldering to make things easier.


Notice that because of the way the components are placed, even if the leads are pinched together, there won't be a short circuit - at least, it helps to minimize the risk. Better yet would be to place heat shrink over one of the wires but as you will see later, I'm doing it differently.


Prepping the next set of connections.


The wires are cut to length, stripped and twisted together.


Tin the wires and cut the ends off cleanly.


The double wires make things a little bulky, but it will work out.


So far, so good.


Make use of the old servo cable.

The signal wire in this cable serves no purpose for the LEDs so it gets snipped right next to the plug and then peeled right off.


Prep the wires for soldering. Remember that grey is negative. Don't forget about heat shrink (yes, I'm using it here). Also note how the wire lengths are staggered to help reduce the chance of shorts.


Slide the heat shrink onto the wire before you solder that connection (I still forget to do that sometimes!). In this connection, I have slid the thin heat shrink over the grey wire only and the thick heat shrink is slid over both wires. Slide the thin shrink over the soldered connection and shrink it. Then slide the thicker shrink over both the thin shrink and the other connection.


Heat shrink is cut to length to cover up the LEDs and resistors. This size of heat shrink won't easily fit over the LED so I stretched it a little wider by sliding it over my pliers and opening it slightly.


A coat of liquid electrical tape or plasti dip is how I have chosen to insulate around the resistor and LED junction before the heat shrink goes on.


Heat shrink in place and showing off some light!


The completed LED string. Shown next to a Remote-Switch-For-LED-Lighting (http://scalebuildersguild.com/forum/showthread.php?20030-Remote-Switch-For-LED-Lighting) that could be used to remotely operate the lights.

Happy Soldering!

matt c
01-12-2013, 11:37 PM
I really could have used this tutorial about 6 years ago. I did way too much messin' around trying to figure this out. Then someone mentioned the resistor. I don't blow up near as many led's now. I even designed a circuit to bright and dim an LED with an enertia switch and extra resister.

I love that little soldier jig! That's what I'm taking away from this tutorial today. Thanks Al!

01-13-2013, 02:12 AM
Great tutorial!! I have been using WAY TOO much wire!! This answers just about all my LED questions and now I can make my trucks a little neater!! Thank you very much!!!!!!!!

01-13-2013, 05:58 AM
I'm glad you guys like this.

Maybe I should start selling LEDs and resistors so you guys can get started making more lights!

Matt, what solder jig? The solder roll holder? If that's what you meant, I agree - That little thing has really made doing electronics easier. Just the fact that it can hold the solder in a consistent position makes it so much better. It was really easy to make from scrap bits of aluminum and a piece of delrin rod.

01-13-2013, 06:16 AM
Yep, Many thanks for the Tut. Here's another one not to handy with electronics!

01-13-2013, 09:16 AM
Nicely done Al!!!! 2thumbs

01-13-2013, 09:17 AM
Thanks, guys!

01-13-2013, 01:57 PM
Thanks, Al! I've tried to reduce wire by unsuccessfully running lights in series. Thanks for showing how to do it in parallel.

01-16-2013, 10:06 PM
Greatly appreciated!

But how would one set up LED's on an alternate source like a 9v or AA's? I tried looking it up, but I got way in over my head... :confused:

I want to be able to take off the body but not have a silly wire to unplug all the time.

01-17-2013, 05:03 AM
If you run from AA's, use 6 volts (that means 4 AA cells) and you don't have to change anything.

To run from 9 volts, you need to change the resistor value to compensate for the extra voltage.
This tool makes it really easy to calculate the resistor value:

01-17-2013, 05:05 AM
Great tutorial! Thanks for the writeup, AL!

01-17-2013, 05:06 AM
Thanks very much!

01-17-2013, 01:11 PM
Brilliant tutorial! This has just saved me countless hours of frustration and swearing.

01-17-2013, 02:11 PM
Glad to hear it!

I guess I should offer this:

I have both 5mm and 3mm White and Red LEDs - the very bright kind (don't ask how many mCd they are, I don't know). I also have the resistors for the LEDs to run at 6 volts as per my tutorial.

$1 for a pair of LEDs complete with a pair of resistors. Shipping is extra.

01-17-2013, 02:58 PM
I've heard guys stating that using a resistor on every LED is a MUST. I've wired up a few LED sets and something I have always wondered: If I buy 3.6v LEDs and run them off of 3.6v, why does one need to use the resistor? I never do.. :hmmm:

01-17-2013, 03:09 PM
It might work, but it is not how we are taught to do it.

The LED is a semiconductor junction that has a certain "forward voltage". It is also has a maximum current it can use or it will have a shorter life.

I was going to go on, but did a google search instead and found a great answer. I want to quote from:

Why do you need a resistor with an LED? The short answer: to limit the current in the LED to a safe value.

The long answer: LEDs are semiconductors, diodes in particular. The current flowing in an LED is an exponential function of voltage across the LED. The important part about that for you is that a small change in voltage can produce a huge change in current. That is the most important concept of this article. Resistors aren’t like that. The current and voltage in a resistor are linearly related. That means that a change in voltage will produce a proportional change in current. Current versus voltage is a straight line for a resistor, but not at all for an LED.

Because of this, you can’t say that LEDs have “resistance.” Resistance is defined as the constant ratio of voltage to current in a resistive circuit element. Even worse, there’s no real way to know exactly the relationship between current and voltage for any given LED across all possible voltages other than direct measurement. The exact relationship varies among different colors, different sizes, and even different batches from the same manufacturer. When you buy an LED, it should come with a rating that looks like this: 3.3V @ 20 mA typical. That gives you one point along the operating curve. Usually that’s a safe operating point. You may get a maximum rating in addition. It may be in the form of either a voltage or current. For example, a lot of people report buying “5V blue LEDs.” These are really not rated to operate continuously at 5V in most cases.

The other thing I’d like you to take away from this article is the idea that it’s more useful to talk about driving an LED with a current of a particular size, instead of a voltage. If you know the voltage across an LED, you can not determine the current flowing in it, unless you are operating it at the exact point along the curve that’s described in the specs. Worse, being “off by a little” in the forward voltage can have a drastic effect in the current. So the approach I prefer is to select a current-limiting resistor in order to achieve a target current in the LED.

Most 3mm and 5mm LEDs will operate close to their peak brightness at a drive current of 20 mA. This is a conservative current: it doesn’t exceed most ratings (your specs may vary, or you may not have any specs–in this case 20 mA is a good default guess). In most cases, driving the LED at a higher current will not produce substantial additional light. Instead, the junction (the working parts of the LED) has to dissipate the excess power as heat. Heating the junction will decrease its useful life, and can reduce the output of the LED substantially. Heating it enough will cause catastrophic failure (producing a dark emitting diode).

and he goes on to show a graph that helps explain this. I encourage you to visit the page.

Hope that answers you :)

01-17-2013, 07:45 PM
thats a good read Al, nice thread!!!

matt c
01-17-2013, 08:18 PM
I'd like to add another thanks for the extra info. Very to the point!

02-04-2013, 08:03 PM
Thank you very much for the how-to. I have been buying all my light kits, but I would have gladly made my own knowing this, and will try my hand at it in the future. Thanks again!

02-09-2013, 08:40 AM
Is it the same process if I wanted to wire 4-6 LED's?

02-09-2013, 08:42 AM
Yes, every LED gets its own resistor and you can connect as many as you want that way.

02-09-2013, 08:43 AM
Just continue on in the same way you see in this picture.


02-09-2013, 09:13 AM
Awesome, I'll have to play around with it a little bit and see what I come up with, thanks!

10-16-2013, 03:12 PM
Great tutorial.
Forgive me for a possible silly question, but why are the resistors on the negative side of the LEDs? I've never seen that done before and always thought they need to be on the positive side to limit the current before it goes through the LED, or does this not matter?

10-16-2013, 03:16 PM
Great tutorial.
Forgive me for a possible silly question, but why are the resistors on the negative side of the LEDs? I've never seen that done before and always thought they need to be on the positive side to limit the current before it goes through the LED, or does this not matter?
Thank you.
This is a good question. The answer is that it doesn't matter. These two parts are in series with each other, therefore all the current that flows through the LED has to flow through the resistor. The important thing here is to get the polarity on the LED correct as it won't light up if you get that wrong.


10-16-2013, 03:23 PM
Right, so even though the power going fron the battery to the first LED doesnt have a resistor, the resistance is still there because the current is coming back in a continuous "circle" of the series circuit just between the two LEDs.....right?!!!!

10-16-2013, 03:27 PM
Uh, I think so...
Each LED has a resistor in series with it. You can connect these circuits in parallel with each other.

10-16-2013, 08:44 PM
Thanks for the info. It helps a lot.

Tommy R
12-28-2013, 04:36 PM
Glad to hear it!

I guess I should offer this:

I have both 5mm and 3mm White and Red LEDs - the very bright kind (don't ask how many mCd they are, I don't know). I also have the resistors for the LEDs to run at 6 volts as per my tutorial.

$1 for a pair of LEDs complete with a pair of resistors. Shipping is extra.

Al, is this offer still valid? If so, I'm very interested! Also, do you have orange/amber LEDs available?


12-28-2013, 04:38 PM
Al, is this offer still valid? If so, I'm very interested! Also, do you have orange/amber LEDs available?


Sure is. Just send me a PM and I will help you out!

Tommy R
12-29-2013, 08:47 PM
Sure is. Just send me a PM and I will help you out!

Done! Thanks, Al! You've made some great contributions to this hobby. :cool:

04-30-2014, 02:44 AM
Make use of the old servo cable.


Another simple question....don't laugh!!

If looking at any brand of this type of cable and plug from the same angle as in this pic....is the signal wire always in the same position? I have some laying around and the red always seems to be in the middle ie: positive, but the other two are sometimes different colours depending on the brand. Just want to be sure before I start cutting and plugging in!! Cheers.

04-30-2014, 04:11 AM
Yep, they're all the same!

04-30-2014, 05:46 AM
Thanks Matt, much appreciated.

04-30-2014, 06:04 AM
With the cables that I have, the center always seem to be red. The negative lead can be brown or black and the signal lead can be orange or white.

04-30-2014, 03:52 PM
Thanks for the advice.

05-01-2014, 09:55 AM
This is great. thanks for taking the time. We all have our strengths and weeknesses and mine is wiring. I typically purchase pre-wired sets from RC Lighthouse for that plug-n-play experience but I think I could take a stab at it after reading this. Thanks again.

08-15-2015, 09:06 AM
Just want to thank Al for this awesome writeup on wiring LEDs. Purchased the "Brake, Reverse, Driving Light Controller with Auto Hazard Lights" and decided to give wiring the LEDs up a shot. So far so good. Headlights and brake lights wired, liquid electrical tape drying as I type. Hazard lights are next.

http://i1204.photobucket.com/albums/bb406/Spidubic/J2%20Skeleton%20Jeep/20150815_104415_zpsn265kfpe.jpg (http://s1204.photobucket.com/user/Spidubic/media/J2%20Skeleton%20Jeep/20150815_104415_zpsn265kfpe.jpg.html)

Soldering job is not the best but the connections are solid. Wiring my own LEDs is allowing me to keep the wiring short and not have any excess. Nice and neat. Of course the controller is icing on the cake and takes this from just Lights to something cool. Thanks again Al!

08-16-2015, 04:51 AM
I glad this was helpful!
Your lighting looks like it will work well.