He has a 2001 Rodeo (in his profile; thanks for filling it out!)
My best guess is this:
3. Check The Ground At The Alternator Bracket
Here is a link to some other idea's (I'm pretty sure this is an electical issue):
http://www.geocities.com/endre_rl/isuzufaq.htm#faq61
here is a link to someone who had the same thing happen:
http://forum.planetisuzoo.com/viewtopic.php?t=2867&