There is most likely two wires going to the side markers, a positive wire and a negative wire. Use a test light to determine which one is +12v, and cut it a few inches from the light. Then, add a foot or so of wire to the light side wire and run it to the back of the parking light, where you will want to splice (not cut) into the +12v that feeds that light; use your test light here also. This will need to be done on both side of the car. Don't forget to cover/protect the orignal +12v supply for the side markers. Don't want it touching anything and shorting out.
While we are on the subject of lights. Does anyone know how to replace the driver's side parking light next to the directional? I can't for the life of me figure out how to get in there without removing the headlight. I tried accessing it via the fog lamp opening, but it is cover with plastic it appears. Any help would be appreciated.