Trying to tap rear speaker for axis box

[LIL400hpsrt4]

Im trying to hook up a sub/amp with this axis box.It intercepts a signal from the rear speakers and sends to the amp. Normally you just tap into the rear speaker wires to the axis box, then the rca's, remote and ground to the amp. I pulled the plastic off and took a look at the speakers and connections but i cant tell which are the + and - on each door speaker. I found a tan/yellow, and tan/white in both rear doors. If anyone could help me decifer which is + n - that would be great. Also would i be able to tap into the factory sub/amp instead? So far i have power and ground to the amp but the signal sounds really weak. The aftermarket sub is barely moving even with every adjustment turned up. I dont know if there is any other way to hook up a aftermarket sub/amp to the stock 6disc changer.

 

[LIL400hpsrt4]

so no one has hooked up a sub/amp to the stock cd player I take it?

 

[JUST4FUN]

why not use a meter set to DC to figure it out

 

[LIL400hpsrt4]

I just tapped into the back of the cd player where I knew for certian the + and -. I have to still run the remote wire but hopefully everything works the right.