can't tell you how to fix but I can tell you what happened. The serial data bus (which includes the security system) goes through the head unit. When you cut wires, the car thinks itself or some component is being stolen, so it locks everything down. Our resident expert on this is Ron93. Crutchfield sells adapters and harnesses.I have a 2005 Cadillac STS with a 4.6 l V8 and I was trying to install some subwoofers and an amp in the trunk without having to take apart the dashboard I just ran it off the speaker wires that went to the sub in the back and when I was done hooking it up for some reason my radio doesn't come on now and my car won't start. It's trying to start but it seems like it's not getting spark or fuel. I already checked the radio fuse and replaced it even though it didn't look like it was blown. What else could it be.?