You will now solder the other end of your wires to the solder points for the left mouse button switch. You should really use a multimeter as recommended in the instructable I referenced at the top to see which solder points you should solder to. This will tell you which solder points will allow current to flow through when the switch is closed. I did not have a multimeter, so I guessed....wrongly. I had to take this apart again and resolder the wires. The red wire is correct in the picture, the white wire needs to be moved to the centre solder point.