In just a few minutes, make your Jeep Wrangler JK fender flare mounted side markers blink with your turn signal. Unlike the "single wire" method, this will work even when your headlights/parking lights are off.
-Simply splice the two wires from the side-marker (one white with green line and one black) into two wires from the turn signal (one white and one white with green line). It doesn't matter which wire from the side-marker is spliced to the white or white with green line from the front turn signal.
Once done, they will be off when your lights are off, on steady when your lights are on, but will blink when you turn on the turn signal on that side either way. If you do have your lights on, the side marker on that side will blink alternately with the turn signal.
Other methods I've seen result in the side markers only working as blinkers if your headlights or parking lights are on. Doing it the way I've done here is no more difficult and will retain all functionality of the side marker, but is not dependent upon your headlights or parking lights being on.
