Power loss problem

I have a 2002 mazda protege and from the day i got it I put my system in that i had installed in my old car. i drove it for about 6 months with no problems. Suddenly when i would come to a stop my radio would power off. It would not just shut off, it would power off and say good bye on the display of my Jvc head unit. This is something that would happen at diffrent times according to how loud i was listening to the radio, and what i was running (like hedlights, a/c, etc.). when i was listening LOUD it would cut off immedietly, but when i started back it would turn back on (sometimes without my subs on, just the head unit).

Since at the time i didn't have the money or the time to fix it i just pulled the box, amp and cap out of my trunk and went about my business with just my headunit. Just today i was standing outside of where i work with a few friends and listening to my radio while my car was running and i think the a/c and headlights were on. I got into my car and took off and when i pressed my break the radio powered off. Keep in mind i haven't had my subs in my car for about 7 months. once i got on the interstate the lights got brighter and i could run the a/c and radio at the same time.

Is this a problem with my alternator, or do I need a bigger battery. I desperately need to put my system back in my car. I spent alot of cash on it and miss the beats. any suggestions. i have owned 3 cars with systems and never had this much headache with the system.

BTW. I have a 1 farad cap, which is plenty for the amps i'm pushing. I tried with and without and it seriousely worked better without.

thanks guys

If i were you i would get an optima battery. It sounds like your battery cant handle it. One of my friends could not leave his 94 civic on with the stereo on for ten minutes before it would die, so if he wanted to listen to the stereo he would have to start the car. He didnt even have subs or an amp in it. So i we put in a better battery, so we could put the amp and subs he wanted in. I suggest getting an optima battery they are the best out there and they last forever.

go search online for the "big 3" or the "magic 3" its just the 3 cables from ur battery/alternator, u add onto them so everything runs better, then u can get a yellow top optima battery, (the red top is just like a normal battery, the yellow last 3X longer than normal batteries), and last u gotta change your alternator, for our stock alternators, its probably a 80 amp, which is like 14 amp at idle, if u get a 200amp alternator it'll be maybe 25+ amp at idle, and that should reduce some dimming, but i suggest, u just buy the battery/alternator at once n install them both at the same time

It sounds like your alternator is failing and/or your grounds are insufficient. Since the car initially was working fine I would venture to say that your alternator is likely dying. However, if you are getting the alternator replaced, replace the grounds - also referred to as "The Big 3". In order to take full advantage of any alternator, you must have a proper ground.