DIY: Fit your own onboard compressor

By: Tony Rabbitte, Photography by: Steph Beaton & Tony Rabbitte


Onboard compressed air when you need it—at the push of a button.

Installing An Onboard Air Compressor 1

Whether you're into hard-core four wheel driving or weekend camping with the family, there is one thing every four wheel drive should carry as standard equipment and that's the ability to compress air.

Adjusting tyre-pressures to suit driving conditions, operating diff locks and inflating air-bed mattresses are among the most common uses of these must-have devices.

Compressors suitable for four wheel driving fall into two categories: portable and onboard. The portable varieties are popular as they can be cost-effective and are readily available at just about any automotive parts and accessories outlet but, seriously, you can't beat a good quality onboard system.

It's a common misconception that onboard systems are complicated to install yourself or expensive to have professionally fitted. Well I can tell ya folks, after this DIY, you'll have the confidence to fit-up your own onboard air compressor with ease.

Installing An Onboard Air Compressor 2

I recently upgraded my system to the ARB High Output CKMA12 onboard air kit—and it was dead easy.

The kit comes with a comprehensive installation guide, a complete wiring harness and all the hardware to complete the job. The tools required are minimal and readily available.

The main compressor unit is designed to accommodate flexibility in installation as the base and main body can be manoeuvred into a variety of positions in order to fit into obscure places, if required.

The unit can be used as a stand-alone air compressor for tyre inflation but can also be used to power ARB's Air Locker systems. In fact, the CKMA12 comes pre-wired to plug straight into ARB's Air Locker systems.

Righto, let's get into it!

STEP 1: Decide on a suitable location for the unit

Installing An Onboard Air Compressor Step 1

Most people seem to mount their compressors in the engine compartment, and that's fine, there's no problem with that, however I chose to mount mine in the cargo area in a spare patch of real estate just in front of my fridge.

When I bought my old GQ, the compressor was located inside the rear quarter cavity behind the trim. It was a very handy place to have an onboard compressor, but unfortunately the CKMA12 has different dimensions so will not fit.

When choosing your location, make sure it's going to be easily accessible with an air hose attached. There's nothing more frustrating than battling to reach gear when you need it. Make sure it's well away from excess dust, mud and moisture and mount it high enough so that it won't get swamped every time you cross a river.

STEP 2: Mount the compressor unit

Installing An Onboard Air Compressor Step 2

The CKMA12 comes with a pre-drilled backing plate which can be used as a template to accurately drill four mounting holes. The base of the compressor has four curved slots for easy alignment. Make sure you get the base plate the right way around, it's a bit of an optical illusion.

STEP 3: Fit the T-piece, hose coupling, pressure switch and air filter

Installing An Onboard Air Compressor Step 3

The T-piece and hose coupling are supplied as part of the ARB pump-up kit sold separately.

Apply plumber's tape to the thread of the T-piece and screw it into the outlet port on the compressor manifold. Apply plumbers tape to the thread on the hose coupling thread and screw it into one of the two outlets in the T piece. Apply plumber's tape to the thread on the pressure switch and screw it into the remaining outlet.

STEP 4: Fit the isolation switch

Installing An Onboard Air Compressor Step 4

A lot of four wheel drives have blanks to take rocker switches. Your easiest approach is to utilise one of these if you have them. Choose one that's easy to get to.

STEP 5: Hook up the wiring

Installing An Onboard Air Compressor Step 5

This can be the most intimidating part for many people, but ARB have made it easy by providing a plug and play wiring harness along with an easy to read wiring diagram.

Firstly, feed the five wires on the short loom labelled "isolation switch" through the switch opening in the dash and using the wiring diagram supplied connect them to the back of the switch.

STEP 6: Finding the accessories circuit wires with a test light

Installing An Onboard Air Compressor Step 6

Using a test light, locate the accessory outlet in your vehicle, then splice the red/yellow wire on the smallest loom to the positive wire of the accessory outlet. Now locate the active dash light supply wire and splice the blue/white wire to it..

Now feed the four loose wires with spade connectors on the long loom through the firewall, or other panels if necessary, and assemble them into the plug as per the wiring diagram.

STEP 7: Crimping the electrical terminals

Installing An Onboard Air Compressor Step 7

Feed the remainder of the loom to where the compressor has been mounted and plug the small female plugs into the pressure switch terminals. Then press the two compressor motor plugs together.

Crimp a yellow eye terminal (supplied) to the heavy red wire and the other yellow eye terminal to both the heavy and lighter gauge black wires

STEP 8: Connecting the main positive wire to the battery

Installing An Onboard Air Compressor Step 8

Next, connect the red and black wires to the positive and negative battery terminals, respectively.

STEP 9: Installing the relay

Installing An Onboard Air Compressor Step 9

Plug the relay in and secure with a self-tapping screw to a suitable spot on the vehicle, then cable-tie all wiring and use corrugated split tubing for extra protection.

STEP 10: Finishing up

Installing An Onboard Air Compressor Step 10

Check all your connections then flick the switch to test—and that's pretty much all there is to it.

This is not a complicated installation and well-suited for a DIY enthusiast. As long as you take your time and follow the step-by-step instructions supplied with the kit, you should have it installed easily within a day. Have fun with it. See you on the tracks.

Check out the full feature in issue #117 of Camper Trailer Australia magazine. Subscribe today for all the latest camper trailer news, reviews and travel inspiration.