drains
well that depends on the setup you have, do you have any subs in it, or additional lighting things which could cause a higher draw at times? In a dimming light situation here are the basics to check;
1) battery condition, is it holding a charge
2) alternator output (with the battery in the trunk and that piddly little charge wire it hurts the electrical performance of the car a bit)
3) Are all connections tight and clean at the battery and ground.