h.o alternator dies

I have a 1992 Buick Roadmaster 5.7L (not a LT1) and I installed a 240 amp alternator at 15.6 volts max. These specs are the results from the testing machine before the alternator was installed on my car. I have two Kinetik batteries one 1800HC under the hood and one 2000hc in my trunk. I am running about 2400 watts rms. kicker ZX1500.1 to two 2 ohm L7s and I have a SX700.4 running my rear deck four speakers at 4 ohm each and I have a SX700.4 for my front stage four 3 ohm components sets. I also have a ZX100.2 running two sets of tweeters. Now I have had starting trouble before and now my alternators regulators keep burning up. I have an external regulator installed on my alternator and it is self exciting. The two batteries were run in a parallel. I was told that I only need an isolator if I want to use my system if my car was turned off. But here is the problem when I drive my car within the speed limit my motor never gets higher than 1200 rpm on the streets and 1500 rpm on the freeway. so after I burned up two regulators the guy at the alternator shop told me to get an isolator so I brought a 240 amp GM isolator (the biggest they had) with the ignition post and when they hooked it up he put my main starting battery as my second battery and put the battery in my trunk for my sounds as the main battery. Now since then my car has always started up but I can see the volt meter on the dash say the battery is low until I hit the gas. My head lights are dim until I hit the gas and if I don’t give it a lot of gas it seems to just be very dim in the car at night. If I switched the batteries on the isolator would my sounds die while I am driving? Why did my system not work with out the isolator?

I believe I was encountering this same issue when I was driving my Bronco w/ a 1wire 200a alt. The "self-exciting" regulator only lets the alt charge after a certian rpm. In other words, the alt may not be charging at idle.

You have to make sure the pulley is correct for your application...