If you have a system in your car and your headlights dim uncontrollably your system is not grounded properly.
You need to go to AutoZone/O'Riellys/Advance and get 2 40" ground cables, and one 24" ground cable. Both with eyelits stamped on both ends of them.
Undo the battery ground and resecure it with an eyelit on it, find the closest biggest fattest bolt on the body or frame and remove it. We are using the 24" here.
Grind all of the paint off of the location UNDER the BOLT. I am talking shiny happy ground. Secure the ground from the battery here.
NEXT go to the trunk.
Remove the ground from the amp, find where you are grounded now, undo that.
Again find the biggest fattest tastiest ground closest to you, its usually a seatbelt bolt(usually a Torx bit) or seat bolt itself.
Take the bolt off, grind to bare metal. Grind the threads on the bolt, the bottom of the nut holding the seat on, AND the where the bottom of the ground touches the car.
Here is the best part. Use two grounds and splice them to the ground leading your amp. Yes, splice them, and then use elctrical tape. Your HOUSE is connected to the grid this way it will work!
Use one of the 40"s going to one ground bolt and the other for another ground bolt, no more dimming.
Now, if your ground going to your amp is smaller than the grounds you just installed - get a bigger ground. I will post pics shortly to add to this post.