cars broke please help

Heya I drive a 1999 micra tlthe last few weeks its been guveing me trouble when I am driveing the lights go dull and the radio turns off the car slows down and so does the ac system turn off I changed the battery less than 1 year ago and I also changed the alternator but it has not sorted the problem any 1 know why please help thanks

The problem is not with the battery nor the alternator. When the engine is running, it recharged the battery even if the battery is flat.
Its a wiring problem, loose or poor connection? You have to check the output voltage of the alternator. It should around 13v with engine running.

Also, upgrade your grounds with nice thick cabling and ensure contacts points are all clean & secure.