Just replaced the factory fitted Blaupunkt stereo in a '99 206 with a
kenwood head unit. Easy enough - two iso connectors plugged straight in
and I guessed the 3rd block at the top on the Blaupunkt radio was for
the steering column remote stalk.

Everything works fine and dandy except for no sound from the rear
speakers - obviously fader control is set to middle but fading to rear
reduces the sound to nothing. The speakers are there and did work on
the Blaupunkt.

Looking at the wiring the iso block for the speakers only has 4 wires
in it and these take up the middle four positions on the block which I
assume is front left +'ve and earth and front right -'ve and earth. The
rear speakers were working before so what's going on here? How was
there sound from the rear with only four wires in the block, is a
common earth involved somehow?

Any clues would be much appreciated!