Re Derek's thoughts about multimeters:

While a cheap digital meter (like the $20 Radio Shack unit) may
not be as accurate as a Fluke (which is what I use in my real
job), I don't think it'll hurt the circuitry you are measuring.
Even cheap DVMs have quite high input impedances (10 megohms
or more), and that kind of load should be unnoticeable just
about anywhere in the car's circuitry.

The amps range is a real advantage. There are some pretty-cheap
meters ( < $100) with to amp ranges.  Very handy in automotive work.
Just don't try to measure starter current with them... :-)

Ted Zateslo