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Mostly old school..!
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Discussion Starter #1 (Edited)
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 ½ brightness
Side marker light on ½ 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 ½ brightness
Front fender turn signal blinks full brightness
Side marker light blinks ½ 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 ½” 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 ½ watt Resistors #271-1116
3 Colors 18 gauge wire
Solder
Heat shrink
 

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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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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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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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Mostly old school..!
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Discussion Starter #8 (Edited)
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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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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Discussion Starter #10
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.
:rofl2:..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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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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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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Discussion Starter #13
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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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?

This image has been resized. Click this bar to view the full image.
 

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Discussion Starter #15
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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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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