Blinking Side Marker Lights

Just gonna leave this old thread here in case anyone wants to do this. Most time-consuming thing for me was
running wires from the front turn signals to the rear side markers.

http://classicbroncos.com/forums/showthread.php?t=198327

Expect problems if you run LEDs.
Opposing ground side marker lights were a pretty common thing on GMs back in the 70s. Pretty trick that you can move a single ground wire and lights blink opposing each other or with each other depending on if power is applied in which pattern. A really basic OR circuit,

LEDs are touchy because they only flow current in one direction and block the other. Add in the low current they draw and they can light up with slight voltage leaks that don't affect normal bulbs.