Im not totally sure about this but I would imagine that the harness is located under the headliner. To get the headliner off I think that youve gotta unscrew the plastic trim holding it up there. By the "plastic trim" I mean the trim on the upper part of the door jams. Im not sure what else you will have to do but it should be pretty straight forward.

 

You can add the map light: there is a bracket for it on the windshield header rail. Look it up on scoobymods. To connect the map light, you'd only need to fish one wire from the dome light. The mirror harness probably isn't there, but can be added too.