Make a Guitar Hero Kit for your PC

Step 6 Wire Button wires to Breakout Board

Armed with a listing of which shorts (same as key presses) will result in what keys, we can now hook up the actual buttons in the guitar. I started by globbing on some extra solder to each pin of the breakout board. Next I took a paid of wires for a switch, chose a pair of contacts that would result in a key press on the keypad controller, and soldered the wires for the button to the pins for a key press. You want to try and steer clear of non-alphanumeric keys as much as you can (things like alt, shift, and insert). Symbol keys should be alright.

I'd definitely test each key after hooking it up to make sure you don't get all of them attached and have none of them work. Attach all your other buttons on the guitar to the breakout board, test it, and you should be getting characters typed when you press the buttons on your guitar.