Passenger side headlight will go off until I wiggle the plug wire truck is a 01 6speed? Then comes back on

bad connection in the plug somewhere. You could pull it apart spray some cleaner in there, then plug it and un plug it a few times and see if that helps. Then put some dielctric grease on it and see what happens.

Most likely the plug itself is worn out. I would consider replacing the plug before it melts. I've seen this happen a few times where the plug get weak connection and the plug melts to the headlight bulb socket. Then its a royal pain in the rear to get out and also you possibly lose the headlight bulb too.

Where can you get a plug and how hard to change

Any part store. Cut off the old plug and wire back to the same pins as it was on the stock plug. Like the batch I got from Autozone fairly cheap and just wire them on.

What's the easiest way to get to the old plug ?

Pull the battery out. You should have enough access.

Ok didn't know if I'd have to pull the tray out or not

You could but it will be a bit troublesome being the bolts are on the bottom of the fender. You got to lay on the ground and bolts are most likely rusted in place and will break the clips.