common ground speakers

[George Nimmer]

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It appears as if the audi 4kq's have "common ground" speaker wiring?
Are these chassis grounded?

I'm installing a new stereo (Blaupunkt Heidelberg) into the '84 4kq, and
this new stereo has the expected + and - connections for each speaker.
How do I wire this up properly to the existing common grounded
speakers?   Do I need to rewire all the speakers or is there an easier
way?  I really want to avoid damaging the speakers and/or the new
stereo.

TIA!
George
'84 4kq
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