I want to connect my mp3 player with car stereo. How?

My English is weak so please forget if there is any mistake.

I have a sony wx c570 car stereo. I tried to connect my mp3 player to car stereo through "BUS Audio in" but its no not working. I also use the AUX but when I connect MP3 player to my car stereo, my car stereo turns off and doesn't turns on until I remove AUX pin. When I remove AUX pin, my stereo turns on.
What is the issue can be???
What should i do?