[scottfab]

Dave,
It would seem to me now that you've verified a good battery source that the next move is obvious. Rather than guess and do a hit-or miss approach why not just measure on one of the known faulty systems?

The courtesy lamps would seem a good choice. They are right there easy to get at. The goal is to determine if you missing ground or 12V at the lamp. From there you continue you hunt for the cause of one or the other, ground or 12v missing.

Steps:
1. take cover off one of the courtesy lamps.
2. remove bulb
3. place the black probe (important) right on the Neg post of the battery.
4. Measure inside the lamp socket on both contact points.
Either contact have 12V? If No then next step is to find out why so you can stop here. Next steps (not listed) would be 12V supply line troubleshooting.
5. If you have 12V on stop 4 then remove the probe on the Neg post of the battery and place the red probe directly on the Pos post of the battery.
6. Now probe the two lamp socket contacts with the black probe. Do you get 12V on one of the contacts? At this point if you get no 12V your missing the ground at the socket. Next step is ground fault isolation.

Since the courtesy lamp does not come on when you open the door you have to be missing ground or 12V (unless all bulbs are popped)
Let us know which one.........