Having ARBs installed in my 95 Wrangler meant on-board air was not just a convenience for me. It meant air was a necessity. I originally used the electric ARB compressor for the lockers and to air up tires. After a couple of ARB compressor failures, I decided to change to a belt driven compressor. This page contains a description of my on-board air setup.
Air Filter - The air filter pictured above is a K&N filter of some sort. Bud had it laying around in his garage so we used it. You certainly don't need anything fancy here. Most just use any cheap filter. I've even seen one fellow use a tiny little square filter element, with no cover or anything. Mine is mounted on a bracket that bolts to the compressor.
Tool Oiler - There are many kinds. The one pictured above is a ten dollar tool oiler and works just fine. As far as the seal between the filter and oiler, don't worry. This is not high pressure so just a decent seal is necessary. Nothing like your output side. The filter and oiler do not have to be mounted together and can have a length of hose in between if you like. In the picture below, you can see Bud's filter and oiler setup. Look along the fire wall. The bright orange canister is the oiler and the air filter is attached to it on the left.
Air Separator - Below (left) is a close-up picture of the air separator. Not because I wanted you to see the separator, but because I wanted you to see the "T". That T is the first connection from my compressor output. A small length of hose connects it to the compressor. One line goes back to my firewall and connects to another T. There it splits off with one line to each nerf bar. The reason the air separator is located where it is, is to clean the air not only from the compressor, but from the air banks (nerfs) also. When the compressor is not running, you are sucking air from the banks. It is important to clean the air from the tanks in case there is any condensation in the tanks. Which of course is common. Also pictured below (right) is the T connection and cutoff valves to each line to the nerf bars. The reason these were installed was to isolate a failed bank if necessary. Should both of my nerf bars fail, I can shut off both and run my ARBs with the compressor directly and whatever volume the remaining system has in it.
Manifold - From the air separator a line runs to the manifold. The manifold as you can see in the first picture on this page is just a series of Ts. One T goes to the ARB solenoids. I have both solenoids connected together with a very small T, then that T is connected into the manifold. These solenoids are wired to switches in your dash. This is the control valve for air to your differentials. When they are "ON" the solenoids are open and allow air in. When they are "OFF" they close off air to the compressed side and vent the differential side.
Pop Off Valve - This is purely a safety measure. Not absolutely required, but a damn good idea. In the event of a pressure switch failure, this device will vent if the pressure exceeds 125psi. It is purely a mechanical device and requires no wiring. Just a connection to sense the pressure.
Pressure Switch - The pressure switch pictured above came with the purchase of my ARB lockers. The hot wire to the compressor runs through this switch. When the switch detects pressure less than 85 psi, it closes and allows power to the compressor. Once the switch detects 100 psi, it opens again and the compressor is turned off. Most people will use a pressure switch typically found on large compressors. The principle is the same except most of the switches are adjustable. The ARB switch is not adjustable.Quick Connect - The last item you see pictured above is the quick connect. This is where I plug in air hoses. This was an easy place to put it. However, it can be inconvenient since you have to open the hood anytime you need air. I plan to add a connection to the exterior of the vehicle for convenience.
Other sources of onboard air info:
http://www.off-road.com/4x4web/faqs/aircompr.html
http://www.mswin.net/users/cuetips/jAirComp.htm
http://users.success.net/luv2jeep/on-board.html
http://www.jedi.com/obiwan/jeep/yorkair.html
http://www.huv.com/jon/jeep/Air/index.html
http://www.europa.com/~bateman/jeep/78cj5/mods/air/index.html
http://www.sirius.com/~pnasvik/tech/air.html
