406 Coupe Alpine audio Fitting problem, sound to dash tweeters only

I've connected my Alpine 7893R HU to the 406 coupe and It sort of
works , the HU is fully functional ( or so it seems ) but the sound
only comes out of the front fascia tweeters, Any ideas what is going
on???

The connectors which arise from behind the factory Philips 4050 are;

a) 2 blocks sleeved together ... Power and speaker wiring

b) the aerial lead

c) an iso connector with a philips label on it... I asume this is
the CD changer lead

d) smaller block.. I asume the stalk controller

and

e) a 7 in a line connector, only 3 pins connected

Any idead what the 7 pin connector is?

...

Please help.. this is doing my head in

.... Tony