Step 1: Symphony of Destruction
First open the guitar and cut the controller wire off the board.
Then cut the traces to all the switches. (Fret buttons, Strum Switch, Start/Select)
Next open the SIXAXIS and cut the body so that the flat part where the start and select buttons are.
Last cut the guitar body where you want to put the controller.
I positioned it so I can charge and see the controller number above the strap.
Step 2: Solder, Solder and Solder
First of all the controller contacts have to stay plugged in since there are some resistors on the plastic.
Now the pinout for the connector is:
Tie 4 - 7 Which is the left d-pad to tell the game it's the guitar controller
3 - Up Strum
5 - Down Strum
7 - Gnd for Up and Down
8 - PS Button
9 - PS Button
10 - Start/Select Gnd
11 - Select (Also Star power so if you have a mercury switch or a gravity switch for the tilt sensor)
12 - Start
13 - Fret Gnd - 6
15 - Square - Orange - 5
16 - Cross - Blue - 4
17 - Circle - Red - 2
18 - Triangle - Yellow - 3
20 - R2 - Green - 1
13 to 20 are the fret buttons. 1 - 6 is from left to right on the guitar controller board looking from the back with the neck up.
Lastly the whammy bar goes to the left analog and the reset button goes to the red button.