[darkpt06]

Ok well that ground may not be the best ground. thats most likely your issue

i have my sub amp and highs amp grounded to the bolt NEXT to the drop down bolt for your spare tire, and i have no feedback.

the power wire may not be an issue but you maybe limiting your self with power due to the gauge of the wire your using.

for example, i have a One 4gauge power wire running to a Fuse box and from there splits into 2 wires going to my amps.

what you said about the dimming of the lights is a problem that would be fixed by a cap.

If you didnt no or for the people reading this that do not know, caps are used to store extra voltage, that extra voltage is used when you get a spike in power (ie when you subs hit), thus if you do not have a cap, and you getting dimming headlights and gauge lights you would have to purchase one to keep that from happening.

i personally do not have a cap in my car.