Pay close attention to the relay that is used in his drawing. Although it looks like a common 12V automotive relay at first glance, and will use the same socket, electrically it is different. It has TWO 87 outputs and no 87a. It is not as common. It is used primarily for auxiliary lighting kits.
You can use KC Hilites 3300 12 Volt Relay
It has the two 87 outputs that are in the diagram.
Those are the ones I used for my setup. It makes wiring a bit easier if you are using heavy gauge.