1997 4Runner HeadLight Problem

Hello.

I have a 1997 Toytota 4runner. About a month ago i went outside to find my headlights were on and battary was drained. I thought I left the lights on overnight, however the switch was in the off position. THe next few days it was like my car was possessed and the headlights would come on whenever they felt like it.
I took it to my local toyota dealer and they had a hard time finding the problem, Then they installed a new part *that actually signals to turn the lights on*. 600 dollars later I felt the problem was solved.
Until today, I went outside and my headlights are on again. Its very bizzare and hard to figure out. The headlights simply come on whenever they want!

Has anyone had this same problem? Any Ideas? HELP!! HELP!!

Thanks


Rick