Check your room lamp fuse in the underhood fuse box. It's possible that
power may backfeed from elxewhere if this fuse is blown. If your dome
lamp doesn't work properly, that's a very good indicator that this fuse is
Unplug your liftgate latch. If the condition continues, you've just
verified that it has nothing to do with the liftgate switch.
Next, unplug the ETACM (electronic time and alarm control module). If the
problem goes away, you know that the issue is due to the lamps grounding
through the ETACM. If that's the case, go back and verify that all the
fuses that feed the ETACM are in proper working order. If so, you should
next check the ETACM ground G04 behind the left kick panel.
You'll find www.hmaservice.com very helpful. You can view the schematics
for your vehicle (and other information). Simply go to
www.hmaservice.com, register for a free account, and make sure you satisfy
the site requirements. Schematics are in the ETM section.