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
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
