Headlight question

[Mtblack412]

I have a 1986 Chevy Fleetside with a 4 headlight setup. My issue is that on low beams my upper lights are illuminated but when I got to high beams only 3 lights light up. The 2 on the left (looking at the grill) and the bottom on the right. The top right doesn't come on even though it does in low beam. I have replaced that headlight thinking that was the problem and it still has the same problem. I just bought the truck and don't know how the 4 light set up should work. Any thoughts?