Re-posting for others:
Start by upgrading your car generator to something from Liana or Balona... I think Nissan will also fit...
Find generator that fits without modification. Get something above 80 Amperes! (Mehran generator is around 45 to 50 Ampere = (50 Amps x 13 Volts x 0.6 Class AB efficiency) = 390 Watt RMS)
For 2 Subwoofers you need at-least 100 Ampere generator...
Your amplifier does not produce power, it just converts power from car into sound... It needs power which your Mehran generator can not produce! This results in lights dimming, battery damage and low output sound!