63 cdv headlights

[Kim K Kaiser]

over the last 6 months, I have noticed on my head lights,  with the eye thing disengaged.  when I run my brights, they seem to run fine, clicking back and forth to low and high, its fine.  then, after about 10 minutes, it goes from bright to dim, on its own, no oncoming traffic, just clicks to low. and wont allow a return to bright, I can hit it, and it will click to bright but immediately go back to dim.  if I run at dim for 10 minutes or so, I can then go back to bright, and it will stay bright for 5 or so minutes, then it goes back to switching to low.    its almost as if something is getting hot, then, when I let it cool (on low), it will allow me to go back to bright.  

the eye wires are all disengaged from under the dash,  any idea where to start to look at this.. 

Happy New Year to all,,