Wow..The guy just wants to install an Amp and everyone wants to figure out how to swap his head unit. LOL....
To answer the OPs question, it's really simple. You need to provide the amplifier with 4 things:
1 - Power/Ground (Power preferably from the battery. Ground from the chassis near the Amp)
2 - Remote power on signal
3 - High level or low level inputs form your head unit (Low level is better)
4 - Speaker wires out from your new Amp to the speakers
The easiest way to get #2, #3 and even #4 done is to buy one of these:
This connects in-line between your factory head unit and factory wiring connectors requiring NO cutting. It will provide you 4 - low level line out connections for your amp as well as a remote power wire AND a way for you to wire the amp to your new speakers without cutting a single factory wire.
For #1, Run a 4ga wire directly from your battery to the rear of the truck behind the rear seat and use a distribution block to run a smaller gauge (8ga) to your new Amp. this will allow you to add a sub woofer at some point in time if you want to. For the ground, find a good place to drill into the back of the cab for a nice clean ground.
For the speakers, you can actually run 4 new speaker wires from the Amp back up to the harness on the PAC AOEM-FRD24 and cut the high level out speaker wires using them instead of running all new stuff to the speakers. that way, if you decide to sell or trade-in, you can remove everything quick and clean.
Its a really easy job if you take your time and have all of the piece parts ready before you tear into everything. Just make sure you have the Power/Ground wire, the low level RCA cables (you'll need 2 - two channel cables. 14' will do). Buy 100' of 14Ga speaker wire, a good crimping tool and lots of butt connectors or you can solder everything if you want.
Hope this helps.