ok no problem, i was looking at the right service book then. You can view it too and even download it from genie if you like. Their literature is free to the public.
But there isn't much to understand different than any other DC powered system.
12, 24, the concept is the same, just understanding how this one or most of these work isn't too difficult. You have a 24v system but it is divided into 12 and 24v. The 24v circuits are usually reserved for the drive power circuit and pump motor power circuit, the big cables. Now the lower voltages 12 or even 5 in some cases is dedicated to the control circuits, the small wiring. You may see a 24v reading on certain circuits like at the keyswitch but having the service book and schematics helps there. And yes you can use the B- as a ground test point, you can use frame ground too but using the B- is better. Checking for voltages is fine but you may also want to check continuity/resistance through the wire you're checking too to make sure you do not have any bad connections like a bad crimp on a terminal or a broken wire.