Bonnie,
First step, get the original GM Service Manual for your year Elky (mine has a red/yellow cover for the '72) It has wiring diagrams for all models for that year. Next, check Amazon.com for a general book on automotive electrical service. You also might find something at Fry's Electronics as well. Even though modern cars do deal with more and more electronics, these books stay pretty basic, knowing that the typical weekend wrencher is not going to have the tools and expertise to do more complicated repairs. One observation in all things electrical... 95% of the problems I've seen have been caused by poor connections and not a failed part. Another thing to consider is a replacement wiring harness. It's good way to go if you have a lot of issues and want to start fresh. Good luck!
Bill