i had same problem found short
If it's a Jetta sedan, my left taillights were out due to a
short in the wiring.
The short was located in the front fender well, underneath the
plastic lining. The wire to the parking light had come loose and was
touching ground.
fyi: the taillights are on a different circuit than the brake and turn signal
lights.
if you can get your right taillights running (or left, for that matter) you can if need be run a wire from one side to the other. Use the trailer light connectors on the back side of the bracket holding the lamps
there are three electrical male prongs there. tiny female connectors are needed
to utilize them. flip the bracket over and you can identify the hot and ground you need