The gray wire is a common ground to the rear speakers.  If you are putting
in a modern radio, require separate grounds for the speakers or they will
burn up your amp eventually.  If you are keeping old radio and just
replacing speakers you can get away with the three wires but sound quality
will not be best.

On Wed, Jul 13, 2011 at 9:17 PM, HotelWestfalia <zolo@foxinternet.net>wrote:

> Hi to all,
>
> I am connecting speaker wires to the plugs.  RF and LF both have two wires.
>  Simple.  But the set going to the rear are only three wires; Red, Blue,
> Gray.  I assume, one of them belongs to both speakers.
> I have the feeling some of you know this.
> Best wishes,
> Zoltan
>

--
Alan Felder
Austin TX
82 Diesel Westy