This 2002 Ford F150 Super crew pickup came in with the compliant that the dome light would glow and the rear reading lights were always about half bright. If they were manually turned on they worked normally. The glowing/half bright condition was present with the ignition on or for about an hour after the ignition was turned off.
I performed all sorts of testing at the fuse box, the GEM located at the rear of the fuse box and at every interior light in the truck.
This is what I discovered after hours of searching. The next two images are of the side reading light harness connectors.
Notice the orientation of the green wires in the connector bodies.
The two reading light assemblies.
The rear of the two light assemblies.
Enlarging the images will allow you to see that the light assemblies are labeled as left (LH) and right (RH). Unfortunately even though they are labeled they can be installed at either location and in this case they were.
In the end the customer acknowledged that he had removed the headliner to have it recovered and must have put the lights back in in the wrong locations. He had done this nearly a year ago so it did not have that brand new look or smell for me to pick up on.