It works using a regular old VOM on passive guitar wirings. With this test, you do not have to de-string your guitar to test questionable wiring. I tried to write this FAQ assuming that non-electrical engineers would read it. However, I assume you have some technical sense and ability. It is a great book about guitars in general.
Every section is worth reading and the book is worth owning.
Clean the resin off the alligator clips you keep in the storage compartment in your guitar case, and clip the red meter probe to the one alligator clip and the black to the other alligator clip. Be sure the probes make good connection and that resin doesn't get in the way. Life is easy. If you have two wires, you can assume that the humbucker can only be wired as a standard series humbucker, and you can treat it as a single coil for this process. In fact, what you have is one wire to each coil, and they are internally connected.