For the low beams, the power comes from the battery to the ignition switch, to the headlight switch, to the fuse panel for the two circuits.
It's very likely that either part of the ignition switch or headlight switch has "burned out" meaning too much current has overheated the contacts and they have either a) carboned up or b) melted the surrounding plastic so that it interferes with the contacts.
Trace the power with a 12v test light/probe and see where the juice stops.
Hint: The blue wire out of the ignition switch powers the headlight motors and parking lights, heat fan and other switched accessories. The black wire powers the headlights, which is probably where your problem is.
I had the same problem one day as described here:
Hope this helps.
'87 Bertone X1/9 Corsa
'88 VW Vanagon
Olympia, Washington, USA