Ok, first off, I know there are a few different write ups on this subject but none of them use a pcb setup nor do they explain in all that great a detail the correct position of the diodes or resistors or even have a wiring diagram to go by. Credit goes to TJeli and Humboldt for posting the part numbers and basic idea for this write up.
On that note, here goes!
First of all you'll need a few supplies;
(4) rectifier diodes, part # IN4004 -come in 2 packs from Radio Shack, .99c per pack
(4) 560ohm resistors, part # 271-1116 -come in a 5 pack card, .99c per card
(1) 2 pack small square PCB's, part #276-148, 1 board will make both sides
sharp razor knife
soldering iron, I use a 15/30 watt from radio shack
solder, 60/40 rosin core in .032 diameter
22gauge stranded wire, preferably 2 different colors to keep track of where the wires go after covering the PCB
heat shrink tubing large enough to slip over the finished PCB
Start by scoring the PCB board with a razor knife on the front (copper) side of the board, repeat this step on the exact opposite side of the pcb, then move 4 solder holes away and repeat the scoring process on both sides. Take your wire cutters and snap the unused edges off till your left with this, the center piece;
First thing to do is determine the layout of your diodes and resistor on the pcb, be sure to leave some space between each component so you have room to work and solder.
Each pcb will have (1) resistor and (2) rectifier diodes, (1) rectifier diode by itself and (1) rectifier inline with the resistor. The two rectifier diodes connect together at one point, that being the output side of your pcb to the black wire from your LED pigtail.
Easiest way to do this is layout the location of all your connections, hold the pieces to the pcb with tape then flip it over and solder the connections. Make sure that your diode and resistor bodies are on the side without the copper around the holes and that he legs of the diode/resistor come through the side with the copper around the holes, the solder adheres to the copper and not the bare plastic.
Its hard to see in this picture but the rectifier diodes have a silver ring around one end, you want the silver ring ends pointing twards the point where the diodes connect (see schematic below). If your using the radio shack diodes then the end WITHOUT the silver stripe is where power is fed to, the end WITH the silver stripe is the end it flows through, if you reverse this then your pcb WILL NOT work.
Once you flip the board over your going to solder the connections together to allow the current to flow through either 1 path(markers only) or the other (turn signals only) or both in the case of using your marker lights and turn signals together. At this point your going to solder the ends of the rectifier and diode to the pcb so it looks something like this;
Notice that when I soldered to the board I connected each circuit to 2 of the solder holes. In the instance of the connection between the resistor and the diode it was necessary to complete the circuit and for the ends where the wires will attach later it is so when you solder the wires you have a larger mounting point for the wire to adhere to.
Be sure to solder the ends of the individual rectifier diodes together. This step is important as the power from the resistor/diode side feeds low power to the marker lights and the diode only side feeds full power for the turn signals. The two sides must meet up at the end where your + power wire feeds the light as shown above.
Once you have your pcb all soldered together you can begin adding the wires that will attach to your factory harness. On mine I used 22gauge red and green since thats the same gauge as the pigtails for my marker lights. I soldered green to the turn signal side and red to the marker light side. This is not critical and was simply personal choice. I would recommend using 2 different colored wires as it makes it easy to identify them when installing. Next step is to connect the black wire from your marker lights pigtail to the point where you soldered the two rectifier diodes together. Once your done it will look like this;
Once your finished its time to test the circuit to make sure everything works. Start by connecting the pigtail to the LED light first, then temporarily connect the white wire from the pigtail to a good ground, connect your marker side wire (resistor/diode side) to your Jeep marker light circuit wire, connect your turn signal wire (diode side) to your Jeep turn signal circuit wire.
If everything is hooked up correctly, when you turn your marker lights on the light will run at approximately half power and when the turn signals are used the light will alternate between half and full power just like your stock lights did.
When your marker lights are not on the signals will flash between full power and off just like your stock lights did.
Here is mine on the low power marker light setting;
And here it is on the high power turn signal setting;
Its hard to tell from the pictures but the marker light is actually about 1/2 as bright as the turn signal.
If everything works properly then use tape or heat shrink tubing to cover your pcb and install permanently. On mine I covered the pcb with hot glue then after it had dried I used heat shrink over that and a bit of electrical tape to make the pcb water proof and loom to protect the wiring. Now create an exact copy of the one you just made for the other side as you need to two of these. Any questions post them here and I'll do my best to help.