Audio Systems: weird car stereo problem, pioneer deh 6700, majestic amplifier

Question
Dear Jerry,
I have a Pioneer deh 6700 cd player. 4, 6.5 in. pioneer speakers. and a jl 10w0 sub with a majestic amplifier. (the sub is the only thing being powered by the amp) Im having a problem with it. yesterday the rear speakers were not working fully. they still had a very small amount of bass coming out but no vocals. also, the sub wasnt working either. so i checked the ground for the sub and it seemed fine. so i played with the preout settings on the deck and set them to full instead of subwoofer. now my rear speakers work. but still no sub. so i checked the fuses on the sub and played with the wiring. i had the car on and unplugged an rca cable on the amp, and plugged it back into the amplifier, and the sub worked briefly and then cut out again, so i unplugged the rca cable again from the amp and plugged it back in and same thing again. im thinking that i possibly have a bad rca connection or cables on my amp or deck. which is why i think the sub isnt working but i do not know why the rear speakers do not work when i set the preout on the deck to subwoofer. im really confused. please help me.

-jason

Answer
The owners manual will explain the preouts and what happens with each.
I would guess that the amp needs a better ground or the amp is damaged.
It would be best to remove the amp and benchtest it at this point (or have it benchtested by someone that knows how). This way, you can isolate it from the rest and will be able to tell if it is the amp or something else in the system that is causing this problem.

You might let me know the amp model number if you know it.

I will be out of town till monday.