Not sure if there is a significant change between the 99 and 98, I am making suggestions based on the 99 and the 99 manual.
Anyway the circuit run you want to look at is 8W-44-6 this the ground path to the dome lights. The Dome gets hot from the same circuit that powers the vanity lamps in the visors and the accessory lamps that are on either side of the dome.
8W-44-6 makes it way to the dome light via: the rear hatch lamp, the rear hatch switch (on the 99 its inside the door actuator not on a jamb), either one of the door jamb switches, and rotating the headlight switch.
You can google 8W-44-6 and find the schematics from other websites.
-To test this circuit,
-Disconnect the battery negative terminal
-go to anyone of the door jamb switches and pull it.
-It may be easier to check at the rear hatch lamp assy, as the entire 8W-44-6 is electrically the same
-You will need a volt ohm meter, does not have to be very fancy a Harbor Freight one will do.
- using the ohm meter function, check continuity to chassis ground, if you have an alligator clip, clip the negative probe to chassis ground and check the connections inside the switch.
- with all doors closed and the headlamp switch not rotated, you should have open continuity inside the switch. If you open one of the doors the continuity should go to 1 ohm or less. If you have continuity with all the doors closed and the headlamp switch rotated midway, you have a wire shorted to chassis.
If this is the case, I would unplug the headlamp switch and retest. , then the fun part of finding a hidden short.
Again, make sure the negative battery term is not connected or you will blow the fuse in your volt/ohm meter