A good read on this.
http://www.jeepforum.com/forum/f9/2-wire-leds-3-wire-conversion-write-up-933239/index2.htmlAlso
Here's how I fixed my 2 wire front LEDs:
You'll need an LED rated flasher relay. EP26 or EP27. Cant remember which.
You will need 2 IN4004 Rectifier Diods (PN 276-1103) and 1 560 Ohm 1/2 watt resistor (PN 271-1116) per side. ($3 at radio shack)
The parking lamp circuit gets (in this order) a resistor, then a diod, then on to the LED. The turn circuit gets a diod and then connects to the same side of the LED that you connected the parking lamps to. The other side of the LED goes to the ground wire.
For the side marker lights, I used Leds as well. To make them work, I capped off the factory side marker wiring and connected one wire to the parking lamp circuit and one wire to the turn signal circuit AFTER the diods right along with the front signals.
Results:
Before. Front blinkers would not function with the lights off. With the headlights on, they would act as running lights, then turn off and on to blink. Both green indicator arrows would stay illuminated when the headlights were on (Like I had 2 burned out front blinkers).
After. Works just like stock. With the headlights off, the blinkers flask on and off. With the headlights on, the front blinkers and side markers run at half power. When you turn the blinker on, they flash between the half power and full power. The indicator arrows work just like stock again with the headlights on or off.
I'm an electrical moron, so when I did this a couple months ago, I mocked everything up and tested it before soldering it all together. Some of the things I needed to swap around till it worked right were:
The positive and negative wires for the LEDs
The direction of the Diod
Where to plug in the side markers.
The whole thing took me about 4 hours including testing, soldering, and wrapping the harness in loom and tape. For that, my blinkers work just like stock, and look factory.
Tips
If you don't have one, buy a cheap little probe test light ($2 at harbor freight or autozone). Makes identifying what wire you're working with easy.
Make sure and pick up a box of different size heat shrink tube from harbor freight. There are a lot of solder connections that need the support if you want to avoid wiring problems on a trail rig.
Grab 3 rolls of different colors wire from radio shack.
I took the extra step of adding in 2 pin connectors so I could take the lights off if I wanted to without getting into the harness. Up to you. ($6 at radio shack, and I was there anyway...)
Grab a couple feet of wiring loom from autozone. Protects the wires and strengthens the connections.