Pat;

If you are installing a "new" or remanufactured Delco alt (as I recommend, as these are quality, reliable, and reasonably priced units), you will hopefully not need to perform any diagnostics for a while, but as other poster mentions, a Multimeter is certainly a nice tool to have for troubleshooting electrical issues when they come up...these typically have a continuity beeper which allow for checking and verifying connections while watching where one is probing, and listening for the beep...perfectly adequate ones start at $20, so they wont break the bank either...I should put some more time in on my tech article: http://www.sw-em.com/an_automotive_electrical_primer.htm

See also: http://www.sw-em.com/altkit.htm

Tim; Tnx for recommendation!

Cheers