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check the over ride valve under the dash in the driver side. small black valve just about in line with the steering column, but at the bottom of the dash panel. If not my guess would be bad vac relays at front of engine compartment.
If this suddenly happened with both headlights I think the problem is more likely no vacuum going to the small hoses on the vacuum relays. Could be the override valve under the column, could be a hose fell off, or could be a problem with the valve on the headlight switch.
There's a small hose running to the front of the car which spits into a 'Y' going to the right and left vacuum relays. You may want to check the vacuum just before the split. If a diaphram is leaking on one of the relays that may cause the problem as well.