Antenna Amplifier for 03 Civic

I have an 03 Civic EX, with the stereo antenna built into the rear window. I installed an aftermarket stereo and I was getting poor radio reception. I failed to connect the amplifier remote turn on (low amp) to the power antenna wire from the radio, so the Window Antenna Amp was not turning on. I hooked up the wire and made sure I was getting power (low amp) that would turn on the amp, but I am still getting poor radio signal. My question is, should I be getting a constant 12V on the larger Yellow/Black wire? I am not getting any power to the thicker wire (not the antenna wire itself), which I assume powers the amp. Has anyone else had this problem?

changing to aftermarket radios, you always lose reception. do you have a wire harness or did you hard wire it ? what kind of radio (brand) is it ?

Its a kenwood KDS-290. I used a harness.

well the only wire you really need to worry about is the solid light blue thats the antenna line but there is no harm in giving the blue/white power either