First you need to find yourself a working york. I got mine out of 83 Volvo for 30 bucks from a local yard, before you start ripping and tearing to get your york out you need to make sure you have a working unit before you spend the time to get it out.  Also look at the tag on the front of the york and see what model it is, you want to get the 210 version since they put out the most volume. To test the york turn the clutch and hold your hand over one of the ports, you should feel the air sucking in or pushing out depending on what side you are holding. Once you know it will pump air you need to make sure the clutch works, simply touch the wire to the positive side of a 12v battery and you will hear a click and see the clutch get pulled to the pulley. York's are self grounding so make sure the case is sitting on a good ground to complete the circuit. I had to get 2 yorks to find a good one. the first one i had was blowing an insane amount of oil out of the discharge port and going everywhere. the rings inside must have been bad so i got another york and this one works great, It may not be a bad idea to get a warranty when you purchase your york so you can take it back if yours doesn't work correctly.
 

Next you need to figure out how to mount in your ride. Broncoair.com makes a really cool bracket kit for the 92-96 Broncos that fits real well(see pictures below). As far as i know this is the only kit out there for late model broncos. its a tight fit but fits in nicely and I like the location much better than saborforces(out of business) on the other side of the motor. The hardest part of the whole broncoair install was the p/s pulley, you need to get a ford p/s puller remover tool to get the pulley on and off which can be rented at a local parts store if you dont have one. Also if you are still running the stock intake you will need to raise the air box up about 1/2" so the intake hoses will clear the york fittings. Chris at broncoair is working on making some spacers for this and will include them in the kits. I will eventually install a k&n open filter like whats in there fipk kit which will aid in more clearance when i make the bracket for the filter.

Now you need to figure out what fittings you need, how you are going to run all your air hose, what  size tank you are going to run, and where you are going to mount it. Its a good idea to plan out your system on paper before you start mounting it on the truck to get and idea of what parts you need. here is how i did the manifold with the check valve, pressure switch, and gauge that diverts the air to where its needed. This picture on the left is how I had the manifold setup before I decided to mount the pressure switch under the hood. The picture on the right is how it is now with the switch all I did was add another 3way manifold. The hose on the bottom goes to the front bumper for the disconnect and the top hose goes back to the tank. All i did to mount the manifold assembly is zip tie it to the bracket for the air box which seems to hold everything nicely. Also it is a good idea to pick up a filter for the intake into the compressor so you dont suck in dirt or small animals. I found a filter from k&n that fits perfectly.  There is so many ways you can route your air and everyone does it a little bit different so be creative.

I mounted my 3 gallon tank right under the rear seat under the truck seems to fit perfectly under there. the fitting that is pointed straight down is where i mounted the safety pop off valve and the other fitting is where the hose that comes from the compressor and goes to the rear disconnect connects.

Now all that is left is to wire it all up. I found some nice little rocker switches that fit nicely in the blank area on the instrument cluster bezel. Its a good idea to use the acc circuit to power the relay so you dont leave the switch on by accident and drain the battery.

If all goes well the compressor will turn itself on and off depending on what the pressure is. I have my pressure switch set to come on at 80psi and shut off at just under 125. This is going to vary depending on the weakest part of your system in. In my case my tank is only rated at 125psi so i have a pop off valve set at 125 to release pressure if the compressor fails to shut off.

All this may seem like alot of trouble just to air up tires, but trust me it will pay for itself the first couple times you use it out of the trail. In addition to using it to air up tires you can run air tools with it too. sure its not as good as a shop compressor but it will put out enough air to use a 1/2 impact to remove lugnuts and be aired back up enough before you can swap tires to tighten them back down.

Parts list:
York compressor 210 model
Intake filter for the comp.
Tank
Switch to turn the comp on and off
30amp relay
0-160 pressure gauge
pressure switch
1 way check valve
pop off valve
misc. fittings and 3way or 4way  manifolds
hose
male barb fittings
quick disconnects

Helpful links to other york installs:
http://soderblom.net/bronco/tech/york/
http://www.webejeepin.com/jeep-onboard-air1.htm
http://www.superford.org/registry/index.php?vID=211
http://mybigbronco.com/info/94yorkcompressor.html

York Parts:
Kirby Enterprises