Well I agree the Haynes man. is not very good when it comes to showing the tricks to removing Ex. headlights. I think there is something about Ford headlights from the late 80's/early 90's that makes the water collect because I've seen it on too many. I have done it 4 or 5 times to Bronco II's, Explorers, and a 88-93 Mustang over the years and have had to drill holes sometimes, but other times silicone sealant did the trick. If you offroad, especially mud pits where the front end drops in, you won't want the holes if you can help it.
1. open the hood and remove the plastic dust shield that is on top of the headlight/grille area. Also remove the rubber dust shield if you have one. It's held on by plastic pushpins and they are tough to remove. Flathead screwdriver helps to pry them out but be careful so you don't break them. (on my rig I replaced these pushpins with bolts, washers, and nuts).
2. unscrew the phillips head screws holding the grille in place. Then pop out the grille. It will take some force and it will pop rudely. It's held in by screws on top and some clamps nearer to the bottom.
3. unscrew the phillips head screws holding the headlight in place. They are located on top of the headlight assembly.
4. reach in and unhook the light connections; both for the turn signal and headlight
5. now pop (e.g. pull towards the front of vehicle) out the turn signal headlight assembly. It's hard to do, because it's held in by metal clamps on the bottom, and these clamps are tight.
Once it's out, you can clean it all, and dry the interior of the light. Clean the lens with a de-yellower or 3M plastic cleaner if needed. Pull off the rubber gasket that is around the headlight and clean it. Clean the outside of the headlight where the gasket goes, and inspect it for cracks where water can get in. Sometimes there won't be any cracks and it will look perfect, but still water can get in. Apply sealant there and put the gasket on. You might consider using clamps or some means of holding the rubber gasket to the headlight so the sealant firms better. Let it sit overnight so the sealant firms up. Over the next few weeks observe the lens for moisture esp. after car washes and/or rains. If it is still getting water in it, you'll have to drill. I suggest drilling on both top and bottom of lens housing if you do this.
Sorry if I typed a lot but I hope this helps more than the Haynes does.