on line manuals

I noticed posts about online manuals for 93 and up GMC and was wondering if anyone knew if they were available for older models such as late 70's early 80's. I have a haynes but that only tells me how to get in trouble. It does'nt tell me how to get out of trouble though. An online version would be so much more convenient. Thanks a bunch in advance as I know someone will reply. Thats why this site is soo much more dependable then the "rest"