One problem related to brake sensor has been reported for the 1999 Volkswagen Jetta. The most recently reported issues are listed below.
The brake sensor caused the engine to think the brakes were applied and lose power. The brake system then failed while dirving and the brakes would just lock up. If the 2nd problem happened on the highway I fear I would have been rear ended. Both problems could be relatd. The sensor problem would trigger a dash warning light for the glow plug relay. In general the car has had problems with the brakes for most of the summer.