i agree that your battery might be going bad. But the dimming is probably going to happen anyways. Dimming in my car only fully went away when i got a high output alt and a deep cycle battery. I'm not sure about your amp, but most amps have a protect mode that they go into if there is under voltage or over voltage. And to clear it up, the battery supplys the power to the rest of the car. The alt. recharges the battery, so if the load on the battery is more than the alt. can handle, the battery gets drained and can cause dimming and sometimes even a rough idle.