Help, flickering lights

So I got my system in last night and I'm running game all 4ga wire I grounded off rear seat made sure to sand down all paint on the bolt and the seat mount , ran a speaker wire to rca input off of the stuck subwoofer wires and used the hi level input on the amp itself. But when my dimmer switch is on anything other than full on the lights flicker, the dome lights as well as the instrument cluster behind the wheel. And all buttons on the hu flicker as well. Did I do something wrong or is there something I've missed? I'm worried to mess the electrical in the truck I don't know a whole lot about audio installation but just enough to be dangerous. I've read about the big 3 upgrade, would that help? Even at low volume with little to no bass the lights flicker. Any input would be very appreciated.

Also it's a 500w kicker dxa500.1 mono block amp 2 hertz 10" subwoofers. I recently upgraded trucksack I had a 14 express and swapped out all speakers and had the subs in there with no issues