Possibly its the headlight lift motor gear and you can see it here http://www.napaonline.com/Search/Detail.aspx?A=BK_6652137_0133254542&An=599001+101999+50060+2060012 and find a shop to replace it here www.repairpal.com/directory
I recently put my 91 back on the road, and to pass inspection I had the same problem [the headlight would not lift up] to deal with. I was not going to spend $250.00 for a new motor. If you are mechanically inclined, I found this site very helpful: http://www.bfranker.badz28.com/headlightfix/ . They offer replacement parts, and instructions. For once, I lucked out with my resolution, 1991's just needed to have the 3 plastic pucks in the housing replaced. They disintegrate over time. I was able to fix it in about 1 hour and it cost me 28 cents to buy a piece of rubber hose cut into 3 1/2 inch pieces to replace the plastic pucks that turn the gear to raise the headlight. Worked like a charm and saved $249.00 Give it a try!