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Old 03-22-2015, 07:16 PM
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The Whole Story About Installing LEDs as Side Marker Lights

There have been a lot of questions concerning replacing side marker lights with two wire LED’s and front fender lights with LED’s when installing new fenders and how they work. I thought I would play around with the schematics, and went out and bench tested what I found to prove it out. Here is the way it works.


The stock wiring between the side marker/turn signal light and the front fender parking/turn signal light uses what is refered to as a floating ground. The front fender lamp has two filaments and three wires. One wire/filament is the parking light hot (+), One wire/filament is the turn signal hot (+). The lamp base/wire is the common ground for both filaments (-).


The stock side marker light has no dedicated ground and is a single filament lamp (two wires) Since an incandescent light bulb doesn’t care which direction it is fed from, they wired one wire from it to the front fender turn signal hot, and the other to the front fender parking light hot.
This means that when the parking lights are off during the day, and you turn the turn signal on power is routed through the side maker lamp at the same time power goes through the front fender turn signal. The side marker light uses it’s opposite wire for a ground through the parking light filament in the front fender. During the day both the side turn signal and front fender light will blink in unison.


At night, when the parking lights are on, it’s just the opposite. The side marker light is getting power from the front parking light circuit, and using the turn signal wire for a ground through the front turn signal filament. When the turn signal is activated also, every time the flasher sends power to the front turn signal it also sends power to the side marker light. This means that the side marker light is seeing the same 12+ volts on both sides and no ground, so it shuts off until the flasher contacts open and the ground is re-established. This is why when the lights are on, the front fender and side marker turn signals alternate.


I tried to explain all this just so that ya’ll would have a little understanding of why there is an issue using LED’s in the side marker location. LED’s do care which direction voltage is coming from and will only work in one direction. Installing an LED in the side marker location using the two existing wires (parking light and turn signal hot’s) will work in some respects but not in others.


Here is what you can expect to see if wired to the existing wires as the original side marker lights were.


LED+ to parking light wire (black/yellow)
LED- to turn signal (right-tan, left-gray)
Lights On: Parking filament front fender on full brightness
Turn signal filament on ˝ brightness
Side marker light on ˝ brightness
Turning on turn signal will cause side marker and front signal to alternate.

Lights Off: Only front fender turn signal will work

LED+ to turn signal (right-tan, left-gray)
LED- to parking light wire (black/yellow)
Lights On: Parking filament front fender on full brightness
Turn signal front fender blinks full brightness
Side marker light does not function at all

Lights Off: Parking filament front fender on ˝ brightness
Front fender turn signal blinks full brightness
Side marker light blinks ˝ brightness

The only way to regain the full function of your side marker light for use with both lights on and off when going to LED’s is to do a resistor/diode mod that allows you to send partial power to the side marker light for the parking light function, and full power for turn signals. The mod is quite easy to do and can be easily accomplished for less than $10 as long as you can solder two wires together. When I did mine I housed it in a little short piece of ˝” plastic tubing and just tie wrapped it to my wiring harness. Just be sure and heat shrink or tape up your connections so they cannot touch each other. Here’s a list of materials available at any Radio Shack.

Jeep LED Front Marker/Turn Signal Light Modification Parts List

Radio Shack Numbers (quantity enough for two harnesses)

4 Rectifier Diodes #IN4004
2 560 Ohm ˝ watt Resistors #271-1116
3 Colors 18 gauge wire
Solder
Heat shrink

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rio lobo and loeb like this.
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Old 03-22-2015, 07:26 PM   #2
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What if you just replaced the side marker bulb with two parallel LED one in each direction

I think them it would work just like non led light does now but in any mode only one or the other led would illuminate

Maybe I have not thought it thru so a test might be on order

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Old 03-22-2015, 07:32 PM
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That would work as long as both were grounded. I know Poison Spider sells three wire LED's which do the same thing, but they are also $30 each. LED Turn Signal 3-Wire | LED Lights | Poison Spyder Customs

Kind of missed where you were going at first....yes, that should work also.
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Old 03-22-2015, 11:34 PM   #4
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I just used the poison spyder 3 wire. They only took a couple minutes to install and have worked great so far
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Old 03-23-2015, 04:01 PM   #5
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Great write up. Thank you.
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Old 03-23-2015, 05:13 PM   #6
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I did a similar thing with a scooter LED tail light. I used a resistor so that the tail light was half brightness, then ran the brake circuit directly to the LED. No diodes necessary.
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Old 03-23-2015, 05:24 PM   #7
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Great write up waterdog. Led side markers have been on the to do list for awhile. I happen to have those wire mid parts lying around too.
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Old 03-23-2015, 05:44 PM
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Originally Posted by 88Hatchy View Post
I did a similar thing with a scooter LED tail light. I used a resistor so that the tail light was half brightness, then ran the brake circuit directly to the LED. No diodes necessary.
What keeps your turn signal from flashing both rear lights if they are tied to the same lead as the tail lights? Or do you mean a "two wheel scooter".... with just the brake light in the center?
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Old 03-25-2015, 10:30 PM   #9
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What keeps your turn signal from flashing both rear lights if they are tied to the same lead as the tail lights? Or do you mean a "two wheel scooter".... with just the brake light in the center?
It was only a brake/ tail light. The theory is the same: use a resistor to dim the LED and bypass the resistor to brighten the LED. No additional diodes are necessary.
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Old 03-25-2015, 10:50 PM
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It was only a brake/ tail light. The theory is the same: use a resistor to dim the LED and bypass the resistor to brighten the LED. No additional diodes are necessary.
..Scooter LED tail light threw me. I thought at first you were talking about a brand of LED....wasn't even thinking of a "scooter"
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Old 03-26-2015, 08:59 AM   #11
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My current game plan is to wire up 2 3-wire LEDs to the front turn signal in parallel. I'll be placing one on the front, and one on the inside of the fender, above the wheel.
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Old 03-26-2015, 06:19 PM   #12
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As long as reverse polarity does not damage LED replacing the stock Marker bulb with 2 LEDs both rated for 12 volts but installed parallel with opposite polarity across the stock 2 marker wires should duplicate stock marker light function as 12 volts in either polarity will illuminate one of the LEDs
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Old 03-26-2015, 06:23 PM
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As long as reverse polarity does not damage LED replacing the stock Marker bulb with 2 LEDs both rated for 12 volts but installed parallel with opposite polarity across the stock 2 marker wires should duplicate stock marker light function as 12 volts in either polarity will illuminate one of the LEDs
Quite true, if you want to use two... or you could use one three wire, or do the mod.
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Old 03-26-2015, 09:20 PM   #14
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I found this picture when searching for ideas for LED side markers for TJs on google. With this 2 light system, would it work to hook one light in parallel with the front running light wire and the second in parallel with the front turn signal wire? If I'm thinking of this right, one would always be on when the running lights are on, and the other would be on only when the turn signal is activated right?

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Old 03-26-2015, 10:35 PM
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I found this picture when searching for ideas for LED side markers for TJs on google. With this 2 light system, would it work to hook one light in parallel with the front running light wire and the second in parallel with the front turn signal wire? If I'm thinking of this right, one would always be on when the running lights are on, and the other would be on only when the turn signal is activated right?
Yes, you could do that. Parking light + and ground, and Turn Signal + and ground.
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Old 07-18-2015, 07:35 PM   #16
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Thank you for writing this up! I just finished the project and all went well.
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Old 07-19-2015, 03:16 PM   #17
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How would you go about installing LED turn signals in the grill but keeping the side markers incandescent?
I mocked everything up. Everything works with the running light OFF, but when you turn the running lights ON the fronts function perfect but when the side marker is very very dim. Shut the running lights off, everything goes back to working order.
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Old 11-07-2015, 08:46 PM   #18
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So with the poison spider leds you don't have to do anything mods correct?
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Old 11-08-2015, 08:56 AM
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So with the poison spider leds you don't have to do anything mods correct?
Just wire them in. White to ground, black to side marker +, Red to turn signal +
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Old 01-20-2016, 11:03 PM   #20
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I am wanting to change my front blinkers and side markers to LED. I have already installed a LED relay. Will I need a resistor for those to work with LED bulbs?
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Old 01-20-2016, 11:25 PM   #21
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In that type of circuit, the purpose of a resistor is to fool an old fashioned electromechanical flasher into working with an LED light that doesn't draw enough current to make the flasher work. That vintage flasher uses the current drawn by an old fashioned incandescent light bulb to make its flasher work. Adding a resistor in parallel with an LED bulb makes it draw more current so the old electromechanical flasher will work.

But a modern electronic flasher designed for LED lights no longer depends on current to make it flash so it works with LED bulbs without the resistor.
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Old 01-21-2016, 08:09 AM   #22
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In that type of circuit, the purpose of a resistor is to fool an old fashioned electromechanical flasher into working with an LED light that doesn't draw enough current to make the flasher work. That vintage flasher uses the current drawn by an old fashioned incandescent light bulb to make its flasher work. Adding a resistor in parallel with an LED bulb makes it draw more current so the old electromechanical flasher will work. But a modern electronic flasher designed for LED lights no longer depends on current to make it flash so it works with LED bulbs without the resistor.
Awesome. Thank you. I didn't want to have to add a resistor so this is good news.
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Old 01-21-2016, 09:06 AM   #23
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Are there differences in LED flashers??

I bought my TJ the Quadratec LED tail lights that come with the EP26 for Christmas. I also bought a LED bulb for the 3rd brake light. Installed it all and everything works perfect. I then decided to put LED in the front/side marker lights and front turn signal lights. Put in the front/side marker lights still everything works perfect. When I put in the front turn signal lights that things go a little crazy. When they are in the right turn signal on the instrument panel is illuminated, The odometer blinks when either turn signal is used and the front driver side turn signal illuminates when the brakes are applied. I have even tried putting the original bulbs back in the side marker lights and kept the turn signal with the LED and the same thing happens. Just curious if I might need a different LED flasher. Thanks!
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Old 01-21-2016, 10:43 AM
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Awesome. Thank you. I didn't want to have to add a resistor so this is good news.
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Originally Posted by Purcell10 View Post
Are there differences in LED flashers??

I bought my TJ the Quadratec LED tail lights that come with the EP26 for Christmas. I also bought a LED bulb for the 3rd brake light. Installed it all and everything works perfect. I then decided to put LED in the front/side marker lights and front turn signal lights. Put in the front/side marker lights still everything works perfect. When I put in the front turn signal lights that things go a little crazy. When they are in the right turn signal on the instrument panel is illuminated, The odometer blinks when either turn signal is used and the front driver side turn signal illuminates when the brakes are applied. I have even tried putting the original bulbs back in the side marker lights and kept the turn signal with the LED and the same thing happens. Just curious if I might need a different LED flasher. Thanks!

There are two separate issues here. As Jerry B. mentioned a resistor used in the tail light/turn signal circuit is sometimes used to add resistance so that the stock flasher unit sees the proper amount of resistance and continues to blink at the normal pace. This is not a good way to accomplish this as it builds a lot of heat. You are better off going with a LED flasher.

The front lights are a different animal. The side marker lights in the fender flares have no dedicated ground and use a single filament bulb for both side marker and turn signal functions. I suggest you reread the second and third paragraph of the first post.

Here's the schematic of the way the front side marker/turn signal is wired.

Since the side marker/turn signal grounds through the front fender lamp filament, and it takes less voltage to operate the front lights if they are led, I think you are going to have issues until you add a dedicated ground to the side marker and use a double filament led bulb or the resistor mod mentioned in the first post which has nothing to do with the flasher, but is meant to give a single filament bulb partial voltage for the parking (side marker) light, and full voltage for the turn signal.
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Old 01-21-2016, 10:59 AM   #25
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There are two separate issues here. As Jerry B. mentioned a resistor used in the tail light/turn signal circuit is sometimes used to add resistance so that the stock flasher unit sees the proper amount of resistance and continues to blink at the normal pace. This is not a good way to accomplish this as it builds a lot of heat. You are better off going with a LED flasher. The front lights are a different animal. The side marker lights in the fender flares have no dedicated ground and use a single filament bulb for both side marker and turn signal functions. I suggest you reread the second and third paragraph of the first post. Here's the schematic of the way the front side marker/turn signal is wired. Since the side marker/turn signal grounds through the front fender lamp filament, and it takes less voltage to operate the front lights if they are led, I think you are going to have issues until you add a dedicated ground to the side marker and use a double filament led bulb or the resistor mod mentioned in the first post which has nothing to do with the flasher, but is meant to give a single filament bulb partial voltage for the parking (side marker) light, and full voltage for the turn signal.
Gotcha. I see what you are saying now. I may not mess with them then. Don't know much about wiring.
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Old 01-21-2016, 12:07 PM   #26
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I can verify the LED side markers I converted a couple years ago work fine with the factory flasher my '04 came with. The LEDs work as running lights and flash with the turn signals as the factory wired the OE side markers to do. I made no wiring modifications, I just had to observe the LED wiring polarity.
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Old 01-21-2016, 12:35 PM   #27
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you can buy the 3 wire LEDs from amazon for $10 a piece. They are the exact same lights that Metal Cloak sells. I put the LED flasher in and everything works great but since I have an '05 LJ, I get a constant beep when the parking lights are on, which I believe is due to the lack of resistance.
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Old 01-21-2016, 01:16 PM   #28
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Hold on there Jerry the factory side markers have two flash modes one with park light on and other with park lights off

One in sync and other opposite sync with turn filaments all via a float ground and one mode current one way and other way current opposite way so no way I see a plain two wire single direction current flow led working same as factory markers

Two in parallel with opposite polarity would
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Old 02-05-2016, 01:47 AM   #29
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I just put in a set i got on ebay for $8 per pair. They are 3 wire. Seem to work ok.
Very dim though.
And the blinking is almost unotivable with headlight on.
I have a 2 wire set as side markets from another company that are 10x brighter

Are the amazone or poison sypder 3 wires really bright?
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Old 02-28-2016, 04:09 PM   #30
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I'm having a difficult time getting my LED turn signals and side markers to work properly. I made the pair of resistor/diode adaptors and have spliced then into the factory harness.

Lights off, left turn: all four LEDs flash in unison (sometimes left side has a quicker flash)
Lights off, right turn: all for LEDs flash in unison (sometimes left side has a quicker flash)

Lights on: all four LEDs steady on

Lights on, left turn: left flash in unison
Lights on, right turn: right flash in unison

I have an EP26 flasher relay. And a replacement multi function switch. Factory flares.

Putting in one factory turn signal bulb in will make the left/right sides flash separately. Though the turn signal and side marker lights will always flash in unison.

Both resisters read 0.55kohm
The diodes read between 0.625-641v and none are "leaking" backwards. Should the range in voltage be closer?

While I know it is fairly simple, this level of electrical is unfamiliar and confusing to me. Am I correct in thinking that I need more resistance when the lights are off?

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