This applies to '02 models, and of course anyone with add-on side markers. If you connect the ground wire of the side marker to the hot wire of the turn signal, the marker will still function as a running light, but will also flash with the turn signals.

It will flash in synch when the parking lights are off, like THIS

and out of synch when the parking lights are on, like THIS

I got the info for this mod from http://lighting.mbz.org/tech/. There is a lot of useful lighting information there.