M and H dash harness 68 GTO
 

Is there any good literature available to explain what each of the various wires from the harness go to-I know they build a lot of extra things into the harness for various options but I would like to know for the things I have to run what wires are for what-some are fairly easy but some a quite baffling and I don't want to just start plugging wires into things if I am not sure

There should be a wiring diagram to the entire car in the shop manual.

I did my whole car with M&H. Very easy to install. If you order the right harness there is little chance of messing it up. Wires are all correct colors and correct connections.