"DanG" wroteI've always been taught to put a test light between the negative
lead and the negative post. Do your same fuse study. If the light is
burning, something is on.
^^^^^^^^^^^^^^^^^^^^
It's not an electrical reason--it has to do with safety. Having the ground
cable dangling in the engine compartment poses no risk of a short (to
ground.) However, I consider an ammeter much better than a light bulb.
It's going to be in series with whatever is draining the battery, which
could cut down the current to a level that doesn't light the bulb. If you
do use a light bulb, use the lowest wattage you can find. Possibly even a
6v bulb in a 12v system.