alpine 7894 = dimming?!

Hey guys,

Fairly new here...question for the pros. I just had an Alpine 7894 installed at the local circuit city. It's powering infinity ref 6x9's and 61/2's in my 01 Dodge Ram.

The truck came with the infinity system, so those speakers were replaced with more decent infinity models. New monster cable 12 ga.speaker wire was run throughout.

Here's my problem. The Alpine dims at about 16 on the volume. The headlights also dim a little bit when the volume is turned up (not super loud but nice)

I called alpine and they said to check to see if the unit was run directly to the battery or fuse panel. I got to the radio, got it out and saw the 12v lead is plugged into the factory harness using a metra kit or something like that.

With that said, I called circuit city and they apologized and said to come on back in and they'll run it directly to the battery. They would not say if this would solve the dimming though. I bought this unit because I thought it would have no problem powering the infinitys. Do I need and external 4 ch amp as well to solve the dimming, or will straight to the battery fix it?? Sorry this was so long, but I feel you guys would give me a straight answer.