Bad wiring
i am guessing that something is wrong with your turn signal switch. Actually, The turn signals and hazard lights are controlled by 2 different relays. Try changing the Turn-signal relay.
hazards and turn signals have separate flashers. replace flasher for turn signals
Check the fuses and the flasher unit.
There are two flashers, one for the hazards and one for the signals.
If the turn signals are inoperative check the hazard switch, if the hazards don't work replace the hazard switch, the signals will start working. if the hazards are ok ,the turn signal switch may be bad.
Turn signals and hazards are two separate curuits. Check/replace your signal light fuse and flasher.
If the 4 Ways/Hazards are disconnected then neither will work the park lights nor the turn signals.
Turn signal flasher module?
you have a bad turn signal flasher.
The 1990 VW Jetta turn signals will not work when the ground wire is broken or corroded. The turn signals may need the lightbulb's replaced.
have you tried replacing the flasher u need to replace the flasher can for the turn signals there are 2 one for hazards and one for turn signals usually found in the fuse box, and cost about 3 bucks
Blown fuse or bad flasher unit. Often, cars use different flasher for the turn signals and the flasher, so it is possible for the hazards to work and not the turn signals.
If your hazards still work, most likely your turn signal relay needs to be replaced.