I am wiring up my truck so that I can blink the marker lights when they are off, and blink the lights, when they are turned on. I have the diagram to do so, but it shows a momentary "normally open" switch in route. Is there a way that a "normally close" switch could be used instead?

 

Radio Shack carries both types for pretty cheap.
I don't se how you could sub one for the other without major wiring changes.

I used a normally closed with a relay on mine, but I only wanted to wink them when they're on.
If they're off, I can just flick the parking lights on and off.

 

You could use a NC switch to control your ground path to your relay off of your marker lights. Turn your marker interrupt switch on and this will kill the ground path to your marker lights.

 

normally open used to turn something on
normally closed used to turn something off