2000 Protege Battery Indicator won't go off and up and down voltage problem
 

I have a 2000 Mazda Protege. The battery indicator light stays on all the time. I have a new alternator and new battery. The alternator is charging the battery. It does have a problem when I first start up the car. The voltage goes up and down so much that the lights on the dash pulse up and down. You can also hear the whole car pulse up and down until the car warms up. Then it stops and the voltage seems to return to normal and the car runs fine after that. The battery indicator light stays on all the time. Whats is causing this? It has been doing this for a LONG time. HELP!

do you have any after market stereo equipment? Check to make sure you dont have a short to ground anywhere.
Check the green wire at the fuse box under the hood , make sure you have good continuity from the alt to the junction box.
Check the PCM/ECU for codes. You may have a "Generator low voltage code."
This happened to me. I removed my after market stereo head unit and fished behind the dash for any loose wiring and found that a wire was rubbing against the one of the metal brackets. I re-located it for the fix.
search this and other Mazda protege forums on the generator low voltage code for more info.
ALSO: Did you replace Alternator with cheapo after market? make sure to use a factory Alt.
I bet there is an issue with the green wire at the UHJB.