Car Hi-Fi help

[paddy27]

i have taken the standard stereo out of my car (Audi A4 Avant 1997) and put my decent sony head unit in.
Unfortuantly Audi in their great wisdom saw fit to make a head unit with no amp for the rears. So i have a power amp somewhere behind some panels in the boot. The problem is that i have a commen return for the two rears,i have the two positive's i need. The head unit says i can't use a common return though.
Are they just saying that or will i do some damage if i split it between the two negatives.
the sony head unit has a pre out for the amp.

Any help would be usefull.

Thanks

Edited by paddy27 on Tuesday 18th August 21:12