[Bru]

I know this is an ancient post, but it may help someone. On the back of the lock cylinder is a plastic cap like Cre is describing. Inside the plastic cap is a sliding quarter-moon shaped copper contact that can become detached from the plastic rivet that moves it when you turn the key. I had the alarm problem on my driver's side door and took the cylinder out to perform the repair. I pushed the quarter-moon shaped clip back onto the rivet and carefully mushroomed the top of the plastic with a small warm blunt rod. Don't go too hot or push too hard or you will melt the plastic too flat and have nothing left to work with. You just want to dome it over a bit to retain the clip. The repair has lasted 25 years as of January 2022.