Had the same problem with my '90 as well.

the wiring harness had burned out - I replaced the harness - avaiable
at any reasonable auot parts store - I got them at Canadian Tire here
in Canada, pep boys would be have them - they are standard for amost
all dual (even if you have GTI four headlamp system your mainlights are
still sealed dual beam) beam systems.

you can check by wiggle the harness at the light a smidge, if they come
on witrh certian pressur in one direction it is a good indication that
the contacts have work away - best to replace them as loose electrical
connections can cause overheating and blown fuses, fires etc.

good luck.