Instructions
Test a game controller by plugging it in and pressing the buttons. Press as many of the buttons at one time as possible, except the directional buttons, to keep your controller working properly after you customize it.
Remove all the screws from the controller with a screwdriver. Take the plastic casing off of the controller to reveal the inner control pad.
Note the paths for the electric current to follow in your controller. See that each rubber button has its own independent pathway and keep only one for your custom game controller. Cancel one of the pathways by drilling a hole through a positive current line, which runs between two dark green lines.
Solder the same number of cable wires as you need buttons on your custom controller to a negative current line in your game controller. Use cables of another color to attach to the positive current lines. Measure your cables prior to installation to ensure the proper length to fit from the solder at the grounding to the switch in the controller.
Check your game controller again by plugging it in to see if touching the ground cable to the positive current allows the buttons to work properly. Apply hot glue to the wires to keep them in place after your game controller checks out.
Attach one positive and one negative cable to a switch inside your controller. Use microswitches or a piece of metal that conducts a current and hot glue the switches in place after you make the connections.