Tom,if you complete the circuit in the manner you described, then you need to have your meter set to measure amperage. In the circuit you described, if you leave the alligator clip connected to the battery and then measure the voltage between the ground and positive terminal of the battery you will get the voltage of the battery, less the voltage drop across your load. In other words, if a fully charged battery has say 12v when not connected to anything, but say 9v when your lights are turned on, that means that your lights, and the wiring in between, are causing a voltage drop of 3v.