first thing to do......check your battery.....is it 1sm or 2sm......if 1sm siya....palit ka ng 2sm kung kasya sa battery cage mo.......second......once applied yung unang step.....try changing your alternator.....risky ang rewinding.....head for a nearest alternator repair shop.....fish for some second hand alternators that are still in good condition and are of higher power rating than your old alternator......the reason why your lights fade everytime your speakers deliver a punch is......that there is not aenough electronic current (DC) running your car........if you apply both of these steps.....this will definitely solve your problem.....:D