Erratic turn signal operation can be a result of a failing turn signal flasher relay which will require replacement.Google+
Car Problem Reports
Volkswagen Jetta TDI Flasher Relay Failure Can Cause Erratic Turn Signal Operation
Volkswagen Jetta TDI Problem
Average Mileage: 177,500 mi (125,000 mi - 230,000 mi)
Visitor, 2001 Volkswagen Jetta TDI, 230,000 mi
It was a cheap 10$ do it yourself fix. My emergency flashers still worked but my turn signals would blink super fast and then stop. The relay is the whole emergency light button. Pry it out with small screw driver and put new one it.
Flashers would work intermittantly and then one would work then fail and vice versa.