I am a newbie to the forum with a headlight problem.
I have a 1985 Nissan King Cab and when I turn on low beam headlights, both sides light up, with passenger side a bit dimmer than drivers side. When I flip to high beam, both high and low beam lights come on as they should for the drivers side but the passenger side high beam light does not come on while the low beam is less bright.
I have replaced both high and low beam bulbs for the passenger side along with the headlight relay located above the fuse block. I have also replaced the headlight fuse.
Any help to solve this problem will be appreciated.

It's probably the ground wire or ground contact on the dim bulb. Check the pin-fit, and for evidence of heating on the ground pin. If those are okay, check the wire and the body ground (the other end of the ground wire) for that headlight.