After spending lots of time on this, I have also discovered that when doors are closed the dome lamp glows, but it is dim. If I pull the dome lamp bulb, the problem goes away, and each fuse acts correctly.
The truck does not have DRL, and I have replaced the mirror switch, the third brake light, the door jamb switches, the headlight switch, and the dimmer switch, with brand new GM parts.
I did pull the door panels, as well as the accordions from the doors to the pillar and saw no cracked, broken or stripped wires. When I look at the schematics, I don't see where these two circuits cross paths. Assuming I want the dome lamp to work correctly, anyone out there have any ideas where to look for the problem?
Thanks in advance!