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I will assume that you are referring to the ones in the tailgate not the dash mounted one. You have to remove the inspection cover on the inside panel (about 8 screws) and, with the window up, you can get to them. There are two one "up" and one "down" The key switch has an arm that activiates either one depending upon which way you turn the key.
It can be difficult and hard to see if you are trying to work inside the truck with the tailgate closed. You can get the window up with the tailgate down by closing the driver's side latch by hand once the gate is open. Make sure you support the window with something before you run it all the way up or it can snap off. That way you can work with the tailgate down and a bit more light on the subject.
Steve83 has an article posted with pictures as to how to deal with a lot of tailgate related repairs. I can never remember the URL for it. Not to worry, he will be along soon enough and is always willing to share.
You won't have to take off the wiper switch on a '93, since it's on the column. The headlight switch can be a pain, though.
Be careful pulling off the instrument panel cover. The plastic tabs break easily.
If you're working on a '93, the instructions in the link in christop43's post won't work. The headlight switch **** and shaft come out as one piece. There's a release button located on the bottom of the switch assembly behind the dash. A major pain in the **** to get to. I've seen experienced mechanics destroy the headlight switches trying to get the **** off of these things. They suck.