On-board Air – ARB CKMA 12 Installed in Nissan Xterra

I recently installed an ARB CKMA 12 compressor under the hood of our Nissan Xterra for the on-board air (OBA) system. Under hood space is extremely limited. That paired with my extremely limited electrical knowledge and complete lack of documentation online (for installing this compressor in this location) made this one of the more complicated and difficult modifications in my opinion.

A lot of lessons learned though… and I did my best below to create a how-to. But honestly… I don’t know if I’d go with the same spot again. It was a royal pain in so many ways to install (in function, it’s great). I found one person who had instead installed this on top of the fuse box in the engine bay. And while I hated that idea, I’d consider that and a lot of other spots before going down the road I did and have outlined below.

One note before I start. What I wrote out are the areas that to me were grey or are specific to this location. By no means should this replace the installation manual included with the compressor. Think of this as a supplement.

Step 1 -Unboxing

I  bought the CKMA 12, inflation kit, and inflator gauge. The compressor weighs a lot more than my old unit and comes with a giant (and intimidating) wiring harness, relay, switch, pressure switch, fittings, backing plate, and a lot more. When you first open it, all you see is the compressor. Once you pull that out and lift the cardboard up it was sitting on, you see the rest. I saw the mess of wires and baggies of small parts and literally thought, “oh shit.” I had a few minutes where I thought of just returning it.

So let me do what I can to help you through that. You’ve got this ;)

Step 2 – Setup

This compressor can be configured in about a million different ways. Which is a huge benefit in that you can tuck it into all kinds of places. But it’s also like a restaurant with a huge menu — in that it’s overwhelming. If you want to go the headlight route, you need to configure it as show and detailed here.

Loosen the two 4mm allen bolts on the blue aluminum mount, and spin the compressor to a point where you can barely use the allen key still. Also slide the the mount all the way towards the end of the compressor with the wiring sticking out.

Next, you’ll use a 10 mm wrench to loosen the bolt on the top of the air tank to rotate it as shown.

Use thread seal tape and connect the air fitting to the hole in the air tank. Quick connect to the top and pressure switch to the side. The air filter goes on the bottom. All these just need to be a pinch tighter than hand-tight.

Step 3 – Mounting

If configured correctly in step 2, you should be able to slide the compressor between the air box and driver’s headlight without touching the air box, headlight or horn (below it). Something like this…

If it doesn’t, go back to step 2 and keep tweaking it until it does. If it does fit, great. Keep reading.

Loosen the hose clamps just pass the MAF sensor. Unclip the air box and lift the entire assembly up and on top of the engine. Take out the air filter. Stick a clean towel in the intake, careful not to push any dirt or dust into the intake. Use a 10 mm wrench to remove the bolt on the outside of the box closest to the firewall and the one inside the air box. The one closest to the headlight doesn’t need to be removed. Lift up and pull the air box out. Now you’ve got room to work.

Next you’ll drill three holes in the center-line of the backing plate. Then match those up on the vertical support and drill those. I took the time to also paint everything. Deathly afraid of rust. To each their own. And then mount it to the vertical support on the grill side of the headlight. I used flat-headed 1/4″ machine screws, nylon locking nuts, washers, and counter-sunk the holes (non of this came with the compressor). The compressor needs to sit flush with the backing plate. Regular bolts would hit before the compressor can sit flush with the backing plate. The end result should look something like this.

Getting the nuts on the backside is a pain. But don’t worry, it gets a lot worse. With the backing plate installed, no you can mount the compressor… sort of. No tricks, wobbles or short-cuts I knew would allow me to mount the compressor to the backing plate with anything more than a 1/32nd turn at a time. So instead I used that 4 mm allen key and pulled the four bolts at the corners of the blue housing out. They’re holding the compressor to the swivel base with rubber isolators. This basically allows you to mount the swivel base to the backing plate (prepare to cuss your way through that), and then the compressor to the swivel base (more cussing).

After all of that, the compressor should be mounted. Ignore the air box — these are “completion” photos.

Step 4 – Wiring harness, part one

Next you need to run the wiring from the compressor to the battery.

Before you do that, you need to strip and crimp on the terminals for the battery connections (all included). Both black wires go to the same terminal ring (negative), and red by itself to positive. I heat shrinked the negative connection since there were two wires. At this point, before you start the install, it’s a good time to put the harness in a loom. Not included and not necessary. It’s what I did because I’m anal about stuff like that.

The harness is not long enough to run from the battery to the firewall, across and back to the compressor… trust me I tried and got to do this part twice. Instead, it will barely reach to go from the compressor, under the headlight to the grill, across, under the passenger headlight to the battery. In fact it barely reaches to the point that you have to connect it from the front side of the battery.

Clip the thick red/black harness into the compressor. Once you know it reaches the compressor and battery, zip-tie it all up.

Step 5 – Wiring harness, part two

Connect the blue and red wires to the pressure switch. It doesn’t matter which goes to which.

Then (if you’re me), add more loom before plugging-in the relay and mounting it (I did mine next to the air box) and run and zip tie the line up to the firewall.

I used the unused port next to the main harness that goes in the drivers side. Simply poke the rubber plug out, drill a small hole, and cuss each terminal through before reinstalling the plug in the firewall and feeding the rest of the harness into the cab.

Step 6 – Intermission

In theory, you’re done under the hood. Reinstall the air box and intake (don’t forget to remove the rag you used to protect it from shit getting in there). When you’re done, it should look like this — not touching anything. If it is, break out the allen key and 10 mm wrench and tweak it until it doesn’t.

The mount here is solid, but does have a forgiving twist due to the mass of the compressor being mounted to a piece of sheet metal. It’s something I might worry about if it was able to move… but it’s tucked in there pretty tight and can’t really move once everything is reinstalled.

Step 7 – Wiring harness, part three

With the harness through the firewall and in the driver’s foot well now — you can follow the included wiring diagram to insert the terminal spades into the included connector. Then connect that connector to the “switches” wiring harness.

If you’re just doing OBA and no lockers, you can neatly tuck away everything except the “isolating switch” harness and the red and blue wires with diodes inline.

Next, remove the driver’s kick panel. There’s an obvious screw at the bottom near the center console. The other is on the opposite side behind some trim. Pull the weather stripping away at the door and carefully un-clip the two pieces of trim to get to that screw. After that, there are a few clips at the top and the whole thing should come off.

Remove the blank. Then use the wiring diagram to connect the isolating switch harness to the switch through the blank’s hole. When done, slide the switch into the blank and install the switch cover.

The blue wire goes to an illumination source. Pin 16 of the power mirror harness is red and is the positive line for the illumination (so it matches all the gauges).

Unplug the power mirror harness and cut away the wire wrap. Isolate pin 16 (make sure you count — there’s more than one red wire in that harness) and tap into it with the blue wire from the switch harness. Wrap it all up with tape, reinstall the harness, and then the kick panel.

The red wire needs a keyed ignition source. I opted for a fuse-tap — it’s the safest in my opinion. But that means making the journey over to the passenger side fuse box. The included wire is not long enough.

Use connectors, solder, whatever to extend the length of the red wire. Heat shrink and use zip ties to route it high and out of the way across the driver’s foot well to the center console. Then use a coat hanger or similar to fish and pull the wire behind the center console to the passenger’s side foot well.

From there, empty your glove box and drop it down (like you do to change your cabin filter… you do change your cabin filter, right?). Run the wire behind the glove box to a fuse tap. I chose the washer pump (same as my dash cam). Heat shrink, zip tie and generally clean everything up and put it back together.

Step 8 – Victory

If everything was done correctly, you can turn your key to ACC or just start the truck. Flip the new compressor switch and listen to that sweet, sweet hum. Hook up your inflation kit and tire inflator… and be the envy of everyone at the end of a trail run.