03 impala there is a factory installed amp all

You might not want to do that. The 760W Pioneer amp might require larger wire due to the power consumption of the amp. Most amplifiers require a direct wire from the battery to the amp. The power wire for the factory amp might not require very large wire and if you tie into the power for that amp the fuse could blow and wiring in your car could melt or catch fire, The best installation is to run the recommended guage wire from the battery directly to the amp with a properly rated in-line fuse.