My battery warning light came on, so I replaced the alternator with a rebuilt one. Now, my warning light goes on very briefly (maybe 50 milliseconds) whenever I turn on my headlights while the engine is running. I find this to be a bit strange. It indicates that the battery is not being charged for that instant the headlights are being turned on. I've never seen this before. Is my rebuilt alternator a dud or is there a problem somewhere else? I'm concerned that if I ignore this, it could lead to a bigger problem.

 

are your battery terminals on correctly/tight enough. mine did that too, and that was the problem. also check the alternator connections since you worked on the alternator.

 

is your belt loose