Re: What is wrong?
I intended to include that Geneh's response is your most likely scenario. Use a DMM to confirm a 4ohm load in bridged mode. It should read 3.2 - 3.8ohms. If your impedence load is correct then check the output voltage of your alternator. At idle it should read 13.5 - 14.2volts and should not exceed 14.8volts at any rpm.
"Acoustics is the study of sound; a branch of physics dealing with sound. The law of physics is constantly challenge. Therefore in relation to acoustics; You must study constantly, for you will be constantly challenged." ...... Rainmanspl