On ALL my other cars, when you pull the seat belt really quickly, it will lock up. But on my Windstar, I could never lock up the seat belt no matter how quickly I pull.

So how do I know that my seatbelt is actually working? Dude, this is really serious safety thing.

On older cars, the activation mechanism was a weighted pendulum. On newer cars, the mechanism is electrically activated and timed to give you a little slack before stopping the unwind.

I supose I didn't really answer your question properly. If you want to test it, try slamming on brakes in a panic-style stop at about 30MPH. You'll see that the belts lock up.