My kenwood kdc-mp235

Question

hello everyone
i have a kenwood kdc-mp235 cd player in my car it plays and sounds great. my problem is when i tried to install my amp the sub woofer preout will not send to my amp.i tried diffrent a v wires and still the same problem i hooked the amp up to a friends car an it played find i also checked the subwoofers and they worked fine.can you guys please help me.