One problem related to brake warning switch has been reported for the 1998 Kia Motor Sportage. The most recently reported issues are listed below.
The brake light first came on and went off for a day or two and then came on steady. Took to dealer and they replaced the abs brake mode solenoid sensor. After 1 week brake light came back on, and then master cylinder went. After 2 weeks brake light came back on for less than a second and went back off. Then last week light came back on for another second and wnet back out. I haven't taken it back to dealer yet.