I have a 2001 Maxima that recently presented the battery and brake lights on the dash. I changed the Alt. tested the battery and then found i have noi low beam headlights. Any thoughts?

 

have you checked the fuse or bulbs yet? If not do so replace a recheck

 

The right side headlight uses one fuse and the left side headlight uses a different fuse. They are located under the hood by the battery. The fuse powers both the low beam and the high beam for that side. If the bright lights work, these fuses are not your problem.

There is a control module under the dash called the SECU that plays a part in the headlights. The SECU uses 3 fuses in the dashboard fuse panel, F10, F13 and I forget the 3rd. But same as above, if the bright lights work, these fuses are not your problem.

I don't know how changing the alternator could have caused this. It is probably an unfortunate coincidence. You could try disconnecting the battery for an hour or so to reset the SECU and see if this solves the problem. Otherwise the headlight switch may have gone bad.