Hello pumpin_up_da,

The most likely cause for the problem you describe is that the remote turn-on lead to the amp is functional only when the head unit is operating in tuner mode. This could be caused by using a power antenna lead instead of a remote lead. Some head units have both, some only one or the other. Check the wire going to the amp remote terminal with a voltmeter. If it shows 12V when the radio is operated in tuner mode but 0V when you switch to CD, then check the wiring. If this is the cause, and your head unit has a dedicated amp turn-on lead, then connect it to the amp terminal. Most head units that have both power antenna and remote leads code them "Blue" and "Blue/White". If your head unit does not have an amp turn-on lead, you need to wire it to a 12V switched source, usually the "red" wire on most aftermarket receivers. You can then put a SPST toggle switch (available at Radio Shack or most auto parts stores) in line with the wire and turn it on and off as desired.

If the correct wire from your head unit is currently connected, then the receiver is defective and needs repair or replacement. Or, if everything else still functions normally, and really don't want to bother with repair or replacement, you can still use the 12V switched source as described above.

Hope this helps.