Headlight problem

[kona_mtb]

on my 1991 explorer xl my headlights work fine in running mode or highbeams but if I put it onto nighttime beams only the left side goes on and the right totally turns off! what is the problem?

 

[Doc Hvac]

there are two different elements in the light bulb one for low beam, and one for high beam start out by eather replacing the blubs or swaping the bulbs around and see if the prob follows one of the blubs