'90 and '93 100Q radio questions

[Don Forte <dforte@mediaone.net>]

I've got a '90 100Q w/a Sony radio installed.  The trouble is that the rear
speakers don't work.  I suspect that there is an amplifier which needs
powering back there, but my Audi shop manual (on microfiche) doesn't
describe the wiring.  Is anyone familiar with this?

Also, I have a '93 w/the original radio that only turns on occasionally.
>From the ads I see for rebuilt ones, I would imagine that this is fairly
common.  I'm thinking of removing it to check the on/off switch.  Does one
simply insert some sort of rod into the 4 holes?  Is there a particular
order required?

If I can't fix it, I'm thinking of a Blaupunkt radio and changer, but
wonder if it's a problem to install an aftermarket on this car, since I
can't find a harness adapter at Crutchfield or elsewhere.

Any help would be appreciated.

Thanks,

Don