whats up everybody, i need some help.

i removed the OEM 816 head unit that was in there ( in know it's the wrong one, some cheap *** installed it before i go the car) i just installed my 7" touchscreen LCD DVD headunit and it's all wired up and sounds great, but i want the surround speakers on the dash to work. the wires are:

light blue / white tracer
light blue / black tracer
black

i'm assuming the light blue with the white tracer is the POS +
the light blue with the black tracer is the NEG -
and the black is the ground

but when i hook these wires up to lets say the left speaker output and ground, i get nothing!

thanks in advance.

 

so i did some research and found that if you go with an aftermarket HU you will lose the suround speakers, but they speak of a dedicated dolby surround amp that will let you use them. what is this and where can i get one?