You can hack into the factory harness, but I would strongly suggest you don't. It's more of a PITA to reach into the dash and try to splice wires together than just buying the wiring harness adapter and doing it on a table then just plugging it in. Then later you won't be kicking yourself if you have to replace the stereo and you have to hack off even more of the short factory wires.
Take the time to do it right the first time and you won't have any issues later. Splice together the wire harness adapter and stereo harness, then solder each joint. I use crimp caps and high quality 3M super 33+ electrical tape. Cheap electrical tape will peal off over time. Some people use heat shrink tubing over the splices but I like butt connectors for not having to heat them.
Nothing sucks like your stereo wires coming loose and blowing fuses when you're driving and need to be somewhere.
Last edited by economichitman; 02-29-2016 at 10:23 AM.