2000 Nissan Pathfinder DASH LIGHT INDICATOR

I have 2 batteries high amps for music system cable zero from alternator (6 months new) positive and negatives, to battery and additional ground cable zero plus factory ground, recently E-brake lights stays on DIM until I pull the e brake where it goes on and battery indicator stays on at start and while driving until I hit 3500 or above lights shutoff anything below that will make it turn on again while driving. I work on my own car since im a student and no job.