first see if the bulbs are getting power going to them, if they are and they won't come on then the bulbs are bad, if they're not getting power then trace the circuit back, which you'd then check the relay, if still no power then you'd check the fuse (could be fuse then relay but you get the idea) then if still you get no 12 volts then you go to the source or "request" which would be the headlight switch. then you'd try known good headlight switch. could be a lot of things, but i'd lean towards corrosion being the culprit being that the car's pretty old.