Need help with stereo installation in 86 5kcst

["Rokas Reipa" <vytas@erols.com>]

Finally decided to pull out the original Blaupunkt head unit from my 86
5kcst and replace it with an Alpine CD head unit(with 35w x 4 channels).
Front speakers work ok, however when I connect the rear speakers, all is
lost. No music comes out of any speakers. The car has the 10 speaker system
with the amplified rear speakers. Does the rear amp need to be bypassed
somehow? Please help. TIA

Rokas
86 5kcst