Sorry if these questions may have been answered already. but it is still confusing to me and since i have spent so much time on it, i would like to finish it off.

the problem.
I have a 91 maxima. 3 speakers(driver side + 2 rear) never worked since i purchased it. took out my rear amps and examined it. had a lot of black coloration around the caps and IC's. replaced the cap and tried it again. didn't work. checked my rear speakers at home and they both work fine. so i purchased 2 rear amps from another 91 infiniti. they look neat and good. when i tried them this is what i noticed.
* my right rear amp was indeed giving out the signal but it was so
weak , i had to hold up the speakers to my ear to hear it, even
on high volumes.
* nothing on the left amp. swapped the 2 amps. nothing on right,
nothing on left.
So i concluded that
* one of the newer amps may be busted, although it *looks* ok.
* maybe there is no audio signal on the left channel at *all*.

since speakers work good (when tested @ home), one amp when connected
to the right speaker gives a faint output, leaves me thinking whether it is the HU causing problems. I am assuming relay is not the cause since my passenger side audio works just fine.

The question is where do i go from here. i really want to get to the bottom of this. thanks for all the help.