Hello. My 1977 CJ5 headlights only work on low beam. When I hit high beam, they go out. The dimmer switch has
been replaced. I tested one of the headlights on another car and the high beam was good.

I checked the 3 prongs and got the following:
headlights off: all negative.
low beam on: middle prong positive, other two negative.
high beam on: all negative.

Does anyone know which of the two remaining prongs should be hot on high beams?

Any idea how to fix this?

thanx