97 jetta 2.0

i need some help i have 97 jetta 2.0 that is barly running but when i take the hot wire offf the altnator it runs fine but if i put battery charger on it on high it will run bad.also now the radio isnt coming on and the air bag light is on.i have replace hall sensor.only code it has in it is the hall sensor is out of range.i have had the alnator tested and it shows to be good