Define "any reason". Cops can be held civilly liable, if not criminally (circumstances dependent) if they make a bad arrest. Besides the fact that a headlight out can be a safety issue, it can also lead to other things such as a drug arrest, someone having a warrant, etc.
Cops are almost never disciplined by their peers and superiors, much less held civilly liable. In the most public cases, if there is a decision in favor of the complainant, the municipality (i.e., TAXPAYERS) pays damages. The cop isn't held personally responsible. Worst case is they get moved to another police dept, like pedophile priests being sent to other parishes and no one knows their history.
The headlight thing is called "pretext" and it's an excuse to go fishing "Mind if I have a look in your trunk?"