since you have a 98 there may not be the cover inside of the trunk lid, if not just open the trunk and looks for the bulbs over the plate, you should be able to see them
if not it I think they just pop out or have the two screws that hold em in
- 95 Mystique LS - Zetec/5spd
- 99 Contour SeVT Sport - Duratec/5spd
Official NE-CEG Contour/Mustang Family