Two problems related to transfer case have been reported for the 1999 Mercury Mountaineer. The most recently reported issues are listed below.
Was driving and the SUV threw itself into 4 wheel drive low, causing rapid deceleration of vehicle. It was raining and it happened without warning. Ford has special service messages #508000 drive line trasfer case concerns. Contact has concerns about not being notified by manufacturer about problem. SUV is at dealer now and is still under warranty. Contact says is is very dangerous when this happens in traffic and rain.
Brakes failed seven times within 70,000 miles. An independent mechanic determined that the gem control module was the problem. When the gem control module malfunctioned, the brakes failed, and the 4-wheel drive didn't operate. Also, windshield wipers operated intermittently.