I posted this once before but the thread sort of went the wrong way so please bear with me as I ask my question again. I hope some of you have experience with this issue:

I have an '89 740 Turbo Wagon. My original tape/radio deck (model # TD-6141) broke once, bought a used one at ebay, installed and works fine. The problem is (and already was before I got the new tape deck) my rear two speakers. The right side one barely crackles, the left one is completely dead. I unscrewed the speaker grids and the speaker dishes look fine - although I didn't pull them out, and there may be something wrong behind them. Then, last night I went for the amplifier, located just over the left knee of the driver (courtesy of a nice brickboard poster), and looked around. Again, nothing looks wrong, all cables are attached and nothing looks loose. So I am stuck - could it be that my amp is internally bad and isn't sending signals (or only bad ones) to my rear speakers? Or is the cabling bad somewhere between tape deck/amp or between amp/speakers?

Any and all help would be greatly appreciated! Also, if anyone can point me to wiring diagrams/FAQs on this issue, please point me the right way. I've searched the archives/FAQs and haven't found this issue.

Thanks.