2001 Volvo S60 alternator

i fixed an alternator in my car ,twice.but from scrap .even that doesn't work .and while my process i took out alternator wire that makes the dash meter off while the car start .The battery light didn't gone .later on i start car fixed back whatever i popup .and think to check by driving.but still the charge in idel position is 12. something and after sometimes charge goes on decrease .i run my car after sometimes (10/20 mins)i run my car later on the battery light came.i gussed the alternator is bad .but may be there's prpblems in wiring .
so let me be clear plz....i have been getting problems with this.....