rear speakers low power factory amp? Help! Options

[joy_zze]

I have a
1999 Celica with 4 6.5" speakers and the little
tweeter in the door. I am pretty sure there is only
one factory amp in the console. For some mysterious
reason, the rear speakers are only getting about 1/4
the power of the front speakers, and very little bass.
I replaced all 6.5 inch speakers with JL audio, and
replaced the head unit with a pioneer mp3 player.
Still, the problem persists. I have double checked the
head unit installation, and all seems to be fine. Is
it possible the factory amp only partially crapped out
on the rear speakers? If so, what should i replace it
with? I don't need anything fancy. The front 4
speakers sound great. I'd just like the rear speakers
to sound as good. Should I (could I) just bypass it? Any help/hints you could offer would
be greatly appreciated, as I am getting quite
frustrated! Thank you in advance, Joy

[joy_zze]

I read that there are blue connectors under the amp that are easily visible unless you are looking at them. Is this what you are referring to, and not the in and out connectors on the left side of the amp. I was in there poking around today, but I didn't see the blue connectors, but then I wasn't looking for them.