Geza,
The previous posts are all good suggestions. I recommend a good digital
voltmeter if you want to hunt down those elusive milli-volts. I constructed
special meter leads for this propose with ten foot lengths and alligator
clips on the ends. Especially useful for reading the voltage drop across
long distances; such as between the positive battery post and the alternator
output or the negative battery post and the alternator case.
Take before and after notes for us.
Good Luck,
Ken Lewis
http://neksiwel.20m.com/