Well you know how I got there. I'd imagine that the power source could be picked up before getting back to the rear where the amp harness is, but I have not looked for it elsewhere. I wanted the preout signals too that fed the OEM amp. You do have a shop manual right? I could have probably tapped into the harness before it got into the back, but the harness before there is tightly wrapped and bundled with not much apparent slack to work with.