[Bob Parmenter]

Michael,

You are correct, it is a circuit. There are some other considerations too. Assuming our discussion here revolves around a rear mounted battery, due to the design of our cars, the longer cable will be the power cable (+) as it goes, usually, to the starter/solenoid, the shorter is the ground (-) since it will go directly to the chassis (usually somewhere near the batt location). The chassis acts as part of the return "cable". Assuming good connections at each electrical consuming device to ground, the chassis offers very low resistence. Given the shorter distance from the battery gound terminal to the chassis, you can get by with less size cable. Larger is better, but not necessarily required. Second, the greater amperage draw is on the power side (e.g. starter). Some of the energy is used by the device to do it's job ( converted to work & heat), thus less energy going back.

Further thought on components working after the cutoff switch is opened; does your power cable have a smaller "pigtail" coming of the terminal ahead of the cutoff switch? If so, that would continue to supply juice even though the main cable is interupted. BTW a cutoff switch in the ground cable loop would open the circuit through the battery for that pigtail as well, disabling the device.