1965 tempest (lights problem??

i have a 65 tempest, and just within the last week when i turn the headlights "on" only the top left light comes on but when i hit the bright lights all 4 come on and i cant think of anything that would make it do this besides the switch on the dash? is there anything im missing, :confused:

nevermind I just found out that the bulbs have more than one filiment (one for high and one for low) "and that was the problem/ and there was some corrosion on the wires (fixed now):smile: