HIDs use a ballast to regulate and increase the voltage for the HID lights. You could have done nothing to your electrical and they still wouldn't have dimmed.

 

Running pretty much the same setup with no dimming as well.
1000rms monoblock and 100x4rms with a yellowtop under the hood and big 3. Using stock 90amp alt.

 

I had a 1995 grand prix with a 120ish amp alternator and when I upgraded the stock power wire from the alt to batt I would say that it was hardly 8 gauge.

To OP, buying a decent battery, some 1/0 connectors and 20ft or so of 1/0 wire would likely be your best place to start.

Anyone buy any 1/0 lately where are the prices at?

 

buy the alternater. wen the car is on everything runs of the alternater