Ok I didn't find what I was looking for in a search and I am at work and don't have access to the shop manual.
I believe that you can just plug the bed harness into the trucks harness and away you go. If I am not mistaken the marker lights just tie into the tail light circuit on each side.
Every GM vehicle that I have ever seen is color coded the same for wiring.
The colors should be the same as the later trucks
http://www.chuckschevytruckpages.com...schematic.html