Seat belt light

Does anybody know how a seat belt warning light on a '66 is supposed to work? I think the light might have been a dealer option. The one in my car currently doesn't work. I had never seen one before I bought my coupe, and I haven't been able to find any information on it. The light is mounted under the dash just below the cigarette lighter and ignition switch.
I'm trying to determine if the light is supposed to be on whenever the seat belts aren't fastened. Does it simply light up to remind you to fasten your belts, and then shut off after a short time? The wiring system seems too simple for it be wired to the seat belts.
I was going to remove the light all together, but after recently seeing one being sold for $95.00 on EBay, I guess maybe it's worth keeping.


Photo of light.
http://forums.stangnet.com/attachment.php?attachmentid=20509&stc=1

My brother had a '72 that, I think, had the same light as your '73. As I remember, it would be on anytime someone sat in the passenger seat and did not have the belt buckled. The seat had to have weight on it to activate the light. That one was more complex than what I have. It had wiring going to the seat and to the seat belts.

I have some type of trashy after-market seat belts in my car now. I don't think the original ones had any additional wiring going to them. I haven't pulled up the carpet yet, but I don't see any signs of any wiring other than that going from the seat belt light to some type of relay mounted just right of the brake pedal assembly.

Great! Thanks!