Most multimeters also have a 10amp meter in them as well. But the test light works also, unless you have a stereo with memory, or anything else that requires constant power, i.e. something with a computer. Remember to disconnect any interior lights that come on with your door ajar.
Pulling the fuses works well as a first step. Hopefully it isolates the problem quickly. Now if you use an ampmeter, you sometimes can get to the problem by what your draw is. i.e. if it is 1-2amps, you are likely looking at a bulb or corrosion somewhere. If it is around 5amps I would look at the alternator. If it is 10amps it is something big. If it is 20amps just look for the smoke.
If you live in the cold, a laser temperature probe can be useful as well. As the wires leading upto the drain will be warmer then the rest of the vehicle.
Before you do anything, the first thing you should do is do a quick once over of your entire truck. Check that all your electrical acc. are working the same as they always did and that your alternator is charging correctly. You need to gather as much info as possible. As I don't know how many times someone mentions something about three weeks into a problem, only to discover that it changes the whole diagnostic procedure, and their problem gets cured in 10 minutes. Everything counts.
