Car Alarms: Interior lights, jumper cables, interior dome

Question
Hello,
My interior dome and door lights on my 99 Yukon are not working properly. When I have the dome light on and then open the door, the dome light turns off or dims very low.

I looked for a bad fuse, but had trouble finding a bad one.  Hope you can help or suggest a solution.
Thanks,

Answer
The only reasons I can fathom would be
1. the battery is low and is not charging.
This is an easy one, charge it up, or
use jumper cables and another car/truck
to quantify the charge. If it restores
the dome light to normal, that's the
trouble, bad battery or connectors.
Could be oxidation on the cables etc..
clean up and or, replace battery. Also
check your charging system.
or,
2. the switch is going bad. This
can happen from over usage, but not
as likely to be the culprit from the
statement "dims or goes out". This
sounds like a power issue.

Check both out and see which it is.

(I am leaning towards the battery simply
from your description).

ALARMTEK