I've searched but can find nothing that exactly answers my question. Tomorrow I am planning on buying either a Pioneer DEH-P9400BH or a DEH-P8400BH and I am curious as to whether or not I need a frame or mounting bracket to install the headunit or does it simply just slide into the same place where the OEM radio was?
Also for the wiring harness adapter, how exactly do I do it so that I don't need to cut the OEM wiring or will I be required to cut it? Thanks in advance for your patience.

 

You're probably trying to be too specific with your searches. Read the DIY AP2 head unit install thread. You'll use the existing brackets and then pop on the trim piece once you're done.

You need a harness for the head unit and a harness for the car. Wire and solder the two to each other.