So a few months back the alternator in my 2000 civic went bad. so I replaced it, i didnt realize fuse 15 had blown under my dash, my speedometer was all funky but i thought it was a faulty vss. I just checked and replaced that fuse and now my speedo is all good but the battery light stays on all the time, I have no problems with any of the electronics in the car not working or acting funny. I have noticed that when I first start the car, the lights are really dim and my wipers are slow, but if I just tap the gas to rev the car up past 2K the lights go how bright they should be and the wipers work fine. Im not sure whats wrong and this was the first place I thought might be able to help me.

 

Check all you connections on your alternator and you engine grounds and main ground.

 

Do this^

It's also possible that the replacement alternator was bad right out of the box.