I have a 4 gauge wire running to a 350W two cannel amp that powers my one 12"rockford fosgate HE sub. I want to install a 4 channel 680W amp to my door speakers. Is it possible to split the 4 gauge wire so that I only have one power cable. This sounds like a bad idea,but I wanted to ask any ways.
yup, that's fine. all you will need is a distribution block. check the "amplifier installation" section of www.sounddomain.com for one. i'm assuming that 680W is max rating. look for a distribution block that has a 4ga input and two 8ga outputs.