Glad I found this site

When in doubt check to make sure you have a good ground connection for your lights. There is a little pigtail behind the grill attached to the radiator support. make sure it is screwed down tight and is not corroded under the screw or against the support. Sometimes with a weak ground you will get enough current to run the smaller lights but when you try the headlights the resistance spikes up and things don't work. Worth a try.