What year Jetta are you referring to? If it happens to be a 1999-2005 Jetta, you can test if the receptor itself is broken by checking the resistance across the wires in the plug under the seat with a multimeter. If the receptor is broken and you don't want to replace it, you can use a resistor from RadioShack or another electronics supply house to trick the control module and turn the dash light off. The four wire plug under the driver's side seat is for the seatbelt. Just bundle the two positives together (usually the red and yellow wires), and the two negatives together (two browns). Then connect with a 470 Ohm, 1/2 watt, 5% tolerance resistor.