Can't receive AM radio,please help

I can't stand it anymore,i miss a lot of good shows on AM but since i installed my aftermarket cd player in my car....forget about it (as they said in Johny Brasco....Forget about it !),the car is a 1995 BMW 318i and i think when i installed my Nakamichi HU (cd 40z) something must have been left out,is it posible that the AM antenna needs to be powered up in order for it to work,the FM is great and i used the right adapter.Can someone tell me what to do,i know there are some wires that i did not use but i didn't think they were needed,what color wire do you guys think it may be,and does it need to be powered or not ?

Thank you

Try changing the connector (plug) on the antenna cable.

If the unit that you removed was OEM and the antenna is also OEM and you had good AM reception then check the resistance of the antenna cable between the plug that goes into the radio and the connector at the antenna.   In some cases, a resistor is installed (in-line) in the antenna cable, usually inside the plug. 

Thank you,i thought i saw 2 types of antenna cable adapters,the one i was recomended it's only a plug change type adapter,but i think there is another one with some kinda tube...maybe that's the one with the resistor in it.

Again,i apreciate your reply

Aftermarket radios are kinda lousy on AM, but it should at least work a little bit.

The antenna adapter with the tube is an amplified antenna adapter.....I've swapped in a few of these and I never heard back from the customer, so I figured it worked.  I'd definitely try one of those.