head unt dims when bass hits

Run the 10 gauge fused power cable from the battery to the constant/memory in the back of your head unit. Also find another source for your ground and upgrade that to a 10 gauge as well make sure that you properly sand it so you are grounding to bare metal. Now in your post above you said that you were running the in dash DVD and some relays off the stock power wires back there. Now that’s probably what’s causing the head to dim but once you upgrade the power cable the dimming should go away.

Yes just put a distribution block on your main 8 gauge power cable so you create a Y. Run one cable to your amp and another one to the mp3 player. Just make sure that your main cable is the correct gauge for the amount off current you are using.