HELP! Engine won't start
 

OK, so I'm installing a new head unit. Everything is going fine until I install this wiring harness/adapter that will allow me to retain the use of my steering wheel controls. (PAC audio's SWI-X) I have my key in the "acc' position, and all of a sudden i lose power. I turn my key to start the engine, and all I get is this rat-a-tat-tat-tat and the service engine soon light. I checked the fuses for the starter, ignition etc, and they are all fine. What did I just fry?

Sounds like a dead battery, or loose conection.