I put some new subs in my 09 fit sport, but my subs are cutting off once I get to a certain volume. It may be to some bad wiring but I want to make sure it's not my car. I've got a 500Watt RMS Mono amp, can the stock alternator power this?

 

If it cuts off, it is likely the amp overheating or not being able to handle that much wattage. A capacitor will help dimming headlights, but not a cut out.

500 watts shouldn't be a problem for the car, but it depends on how much you are drawing for your other speakers & accessories. I have a walmart amp, that can't handle high volume. The cheaper amps typically lie about their max rms rating. Mine is a 4 channel, but I can only run two speakers or it keeps cutting out.

 

Sounds like bad wiring or maybe a bad amp to me