Originally Posted by whitetmw

This is possible. When the load exceeds the available amperage the voltage reading can be 0. Not that there is no voltage, there is just nothing to push it through. This would indicate ( in our case with the Diesels) that one of the two batteries is DOA and insufficient Amperage is Available. I didn't believe it either and was scratching my head when I attended a class Dan Sullivan taught. He demonstrated it and I was amazed.

In essence its just like checking for voltage on the ground side of the electric motor. If the motor has failed or is failing, voltage can be seen on the (-).

Dan "is the man" when it comes to electrical. He has a book out I have somewhere on a shelf I've read no less than 10 or so times. Written for the Technician and not the Engineer (if you know what I mean) focus is on automobiles and heavy machinery. He made a product called the "LoadPro". Changes the whole way you look at electrical troubleshooting problems. That book and tool has paid for itself 100 x over. I'll see If I find it tomorrow I'll post the Title. Its well worth whatever I paid for it because like I said, its paid for itself the first use.