I'm curious where the wiring is that makes the seat belt light come on if your not wearing it

I never had a working blue dingy in all the Fieros I've owned and never really wanted one because of the dinging if the doors were open. After killing my battery a while back when I left my parking lights on I figured I better put one in and live with it! I installed this one I got in a parts lot at e-bay. It's not blue but works great!

I always use my seat belt but I never knew that with this installed the seat belt light will come on and stay lit until you put it on! How does it know? I don't remember any wiring going to the seat belt harness?
[This message has been edited by Gokart (edited 08-01-2007).]