Here is a link to a bunch of glow threads from the "Resources" section at the top of the page.
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread.html#post1019018
I just fixed a glow plug problem with mine. Luckily it was easy. Basically you get a meter and check the plugs, relay, fuses and wiring. On the 6 cyl. they can be a pain because of the intake.