Cab-clearance light wiring?

[Moloko]

I've been working the last few nights on getting my 85 K20 to have all it's lights working. It had a plow on it, and when the last owner removed the plow lights, he made nothing but the side marker lights and tail lights work. I fixed the headlights, turn signals, etc. All that isn't working is the cab lights on the top of the cab. Where does the wiring for these come down at, and where does it go to? I have looked in a few wiring diagrams, and it's never mentioned. I have no problem running a new circuit if I have to, but I'd like to know where the factory path is before I start tearing into stuff.