no lights in cab or sleeper

Take off your sunglasses! J/K Sounds like a relay problem.

 

I was looking at the fuse diagram apparently there's not a relay for interior lights. Take a look at the diagram below and try swapping 20A fuses marked in RED, if it works one of the fuse is blown. Hope this helps.

 

You probably have some fuses in the sleeper. Id get a test light and check all the fuses. Sometimes they look good when they are bad. My pete had a little panel under the A/C controls in the sleeper that had fuses in it.

 

I'm having the same issue on my KW only mine works on and off

 

There are no fuses in the bunk so you can save some time not looking anymore. The only fuse in my 97 in for an acc. port 20a inline.

Try checking the fuse panel with a volt meter in place of the fuse for the lighting, it's possible there could be corroded terminals behind the fusebox itself if there ever was a leaky windshield. Also pull the glove box and check the roof harness ground, it is to the right bolted to the aluminum dash extrusion just below the glove box. chances are it is covered in light green corrosion.

 

Check behind sleeper controls. Should find the main wire harness for the sleeper. Check door switch for power. Think the harness runs behind interior on driver side of cab. Then back to the left side of sleeper.