I got mine from Crutchfield, but I don't think it is in the catalog.
The rep I ordered the receiver from told me about the single wire
problem and offered this solution.  I'd have to dig out the wiring
diagram to be sure, but as I recall all the ground wires from the
receiver connected individually, then you splice all the speaker grounds
together and connect them to a single connector on the unit and
everything magically works.

I'm no electrical engineer, but it appears that the unit balances all
the return current flow across all four receiver grounds, preventing the
excess current flow caused by shorting out two of the grounds by
connecting them to the single wire.  I'll check tonight for sure.

Kent Tunks wrote:
>
> I was not aware that a ground isolater was available for a common
> speaker wire.What
> exactly does it do electronically?Also ,where can you you get one?
> My 86 Vanagon,a Country Homes camper,came with a common ground wire for
> the rear
> speakers.This caused me to blow up one radio before I realized what the
> problem was.
>
> If I recall correctly,it was wired in such a way that at tha radio
> end,there WERE two
> wires for each speaker!The two common wires at the radio end were
> multed(joined
> together) somewhere where it was not easily noticable.
>
> It finally took a meter to figure out what was going on.
>
> Kent Tunks

--
Stuart MacMillan
Seattle

'84 Vanagon Westfalia
'65 MGB (Driven since 1969)
'74 MGB GT (Restoring)

Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)

Parts cars:
'68 & '73 MGB, '67 MGB GT