I have a very mild Pioneer 45W X 4 cd head unit installed using a factory wiring harness adapter and I notice that above 1/2 volume the display on the head unit dims with the bass and the sound is a bit distorted. Is the stock wiring/fusing too small for even this small upgrade?

I was thinking of using a different 12V feed for the main power, any good sources already under the dash or should I just go to the battery?