Pull the rope thing and disengage your garage door from the chain. Then hit the button to close the door. See if the motor would stop after some distance. If it does then it just mean that your chains skipped or something. You would need to take it off and adjust it so that when it stops your door meets the floor.
If it doesn't... I don't know, buy another one.
Here's one on my car.
http://upload.3sgtemr2.com/upload/necowife10.JPG
http://upload.3sgtemr2.com/upload/necowife1.JPG
http://upload.3sgtemr2.com/upload/necowife2.JPG
http://upload.3sgtemr2.com/upload/necowife3.JPG
http://upload.3sgtemr2.com/upload/necowife4.JPG
Some semi's on the road here are already outfitted with more then stock lights. They're orange though. So it has been done here. Just on a much lesser scale.
Just have someone go out car shopping with you that knows more about cars. That is, if you want to go the used route. I wouldn't buy new again either. Been there, done that, not again. Unless I get rich. But even so, it would be iffy.