Tech: Installing an ARB Compressor Short Cuts
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Author/Photographer: Ray Sala | Editor: Phil Hansford, August 8, 2001.

Subject Vehicle: 1989 Mitsubishi Montero LWB

After I decided to get an ARB Locker for my 1990 Mitsubishi Montero, I found that I would also need a compressor to provide the necessary air to actuate the locker. While there are numerous choices available, my first priority was to ensure that I could have someone do a reliable installation quickly with a minimum number of problems, i.e. KISS (Keep It Simple Stupid).

I definitely wanted to avoid using a compressor that needed hard to find parts to work with the locker, or have long-term reliability problems down the road. With these goals in mind, I decided to go with a proven solution: an ARB compressor. I decided to have a local shop install the compressor, but the shop I was planning on using was shutting down for a couple of weeks for the upcoming Rubicon Trail Jeep Jamboree.

Unable to find another shop that was inexpensive, close by, and able to do the install in time, I decided to tackle the installation job myself. By doing this, I would also easily save over $350.

ARB Items Used

Tools Used

Materials Used

Compressor Mount (may be optional)

Pipe Fittings Used

Ask Qualified Advice

Selecting Your Installer
Readers should take proper care in selecting their installer. At one shop I was told that the compressor had to be mounted upright. I have since learned from ARB that this was incorrect. ARB only cautions against mounting it in such a way that water might seep into the flat, screw on access panel. I suspect that the shop was either truly ignorant, or they were trying to make a few extra dollars on fabricating a custom mount. Having already built a workable mounting bracket and fitted the Compressor to the rig, I've decided that with a trip deadline fast approaching, I'd go with the horizontal mount for now, and redo the mounting (vertically) once the trip is over.

I first began by asking a number of members of the 4x4wire Trailtalk community as well as ARB themselves for some advice prior to doing anything.

I then decided on where I would mount the unit. My 1990 came without headlamp washers so there is ample space in the front Drivers Side of the engine compartment, which normally houses the tank for the headlamp washer fluid.

Upon closer inspection, I even found that the two threaded holes there normally used for said tank actually matched two of the four mounting holes and the metric threads of the ARB mounting hardware. Using these holes along with the bolts that ARB supplies, one could mount their compressor in that spot vertically.

A local shop informed me that the compressor could only be mounted right side up (see sidebar). I used two 6 long 90-degree steel L braces to mount the compressor right side up.

You'll need a 5/16 steel bit to drill holes into the two braces (2 holes each) along with 4 sets of stainless steel bolts, nuts and lock washers to attach the compressor the L braces through these holes.

I chose to also use the original mounting plate that comes with the compressor for additional bracing where the compressor mounts to the braces.

Bolting It Up

Mounting the Compressor
I began by mounting the compressor & stock mount plate to the L braces, using the four bolts, nuts, & lock washers. Once the compressor & plate were securely mounted to the braces, I then used two of the four metric bolts supplied by ARB to attach everything to the Montero.

Mounting the Solenoid
Once mounted, I first removed one of the side small plugs and treaded in the ARB Solenoid using the Male-to-Male BSPT (British Standard Pipe Thread AKA Metric) connector. Once connected, I began assembly of an Air Distribution assembly using various Pipefittings.

tn_pipe_assy_1.jpg tn_pipe_assy_2.jpg
air assembly option #1 air assembly option #2

Building the Air Distribution Assembly

I initially connected an L fitting to a Male-to-Male converter. I then attached this to the compressors middle NPT hole. Once threaded in place, I then assembled the middle T connector to the lower elbow. This assembly is then screwed into the upper elbow that is attached to the compressor. Once the distribution assembly is completed I attached the ARB Pressure Limit Switch and LP Air Quick Release Fitting.

Mounting the Switches

The switches fit perfectly on the slope in front of the console box

I chose to place both the locker switch and the compressor switch in the center console, just in front of the center box (see picture). Doing this gave me quick & convenient access to turn on both the locker and compressor.

The four screws which hold the console down are visible after you remove the rigid black liner-box

I began by removing the console box. To do so, you'll need to remove the inner black plastic compartment (under the lid), which is snap fitted in place. To remove, first use a screwdriver to carefully pry up the back edge of the console. Slowly work the black box up and out of the unit. Once removed, you will see four screws inside the bottom of the box attaching it to the floor. Remove these screws, being careful not to lose them.Then remove the two exposed screws in the front of the unit, just in front and to the sides of the shifter assembly.

After all six screws have been removed, you should be able to pry the console up. You may have to move the shifter to neutral and back to park as you remove this unit. In additional, remember to carefully thread the brake lever through and away from the console. Once removed, I took the black plastic shifter bezel from the center console and carefully set it aside. Once this was done, I was able to easily use a small rotary cutting tool to carefully cut 2 properly aligned rectangular holes to allow me to mount the two switches.

Caution: Be careful to not to cut the switch holes up too high (as I did), since the switches may interfere with the cover of the console box.

Get All Wired up!

Attaching the Short Wiring Harness to the Switches
With the center console still removed, I ran the corresponding individual connectors from the inside of the center console out through the freshly cut switch holes and attached them to the corresponding switch connection tabs. Double-check your wiring. It is important to wire all switches correctly prior to inserting them in the openings. I made ample use of the included wiring diagrams to accomplish this correctly. Once all wires were connected properly to the switches, I inserted the switches fully into the selected openings, and temporarily set the center console to the floor, being careful again to move the shifter from park to neutral and back.

The legend shows each wire's location

Running the Wires in the Engine Bay
With the compressor mounted, I was able to begin running the wiring loom from the battery to the compressor, and finally into the passenger compartment. I wanted to be sure to use as many of the existing Mitsubishi wire straps as possible, for that OEM look.

I began by removing the 30 Amp fuse from the included in-line fuse holder. Once this was removed, I attached the red power wire to the +12V battery terminal and the black wire to a chassis ground point. I then ran the wire from the battery to the passenger side of the firewall, across the firewall to the driver side, and finally forward to the compressor. Once run, I began attaching the wire to each of the many original steel cable-retaining straps. I found that by doing this, I did not need any additional wire ties to secure this wire.

I then ensured I had enough wire to connect to the compressor, pressure switch and solenoid. No problem - everything fit. Once I found that everything connected fine with no stressed connections, I focused on running the wire into the passenger compartment to attach to the compressor switch and Locker switch. NOTE: None of the wire assemblies are hard wired at this point. I wanted to ensure everything fit properly before committing things.

Running the Wires to the Switches in the Passenger Compartment
I found a large (2 diameter) rubber grommet on the driver's side of the firewall. I cut a small hole (3/16-1/4) into this grommet to allow me to insert the 5 switch wires into the passenger compartment while ensuring the smallest possible opening to minimize dirt and water in the passenger compartment.

Installation Tip:
Do Not strip off the insulation yet. Wait until the wires have been run to the switches.
Cutting the Wiring Harness
In order to fit the 5 leads (with terminals already attached to them) into the hole I made in the grommet, I needed to cut the connector ends off. I cut them at approximately 1 from their respective ends. This would allow me to reuse these spade ends by simply re-attaching them with crimp connectors.

I then carefully inserted the 5 wires together through the grommet into the passenger compartment. I proceeded to feed the wire through until I no longer had any excess in the engine compartment. I moved to the passenger compartment and routed the wire high up in the dash to the center of the firewall and then down and under the center console to where my switches were. I then rechecked the wiring in the engine compartment ensuring nothing was too taught.

Re-Attaching the connector ends
I then stripped back from all the cut ends and re-attached the corresponding colors using crimp on connectors. Once re-attached, I assembled the wires to the plug by inserting each of the 5 spade connectors into their corresponding location in the plug. Pay close attention to the wiring diagram when doing this step. Once assembled, I simply plugged the end I just assembled into the corresponding end that is part of the switch wiring harness.

Connecting To Ignition Power and Light Power
Rather than hunt and peck to find where the ignition power and light power are located, I took the vehicle to a local stereo shop and had them connect these last two wires.

Once this last step was completed, I proceeded to ensure that none of the wires was too tight, and upon finishing this, I disassembled the Air Distribution Assembly for the last time to allow me to re-assemble things with Plumbers Teflon Tape.

Getting Some Fresh Air to the Air Locker

I began by threading the blue tubing through a clear vinyl tube (3/8 I.D.) that I purchased for a few dollars at a local hardware store. I did this to help protect the blue tube from both the elements and the rigors of off road abuse. To accomplish the threading I simply used water to help lubricate the inside of the clear tube. This allowed the blue tube to slide easily into the clear tube.

Installation Tip:
Special care must be taken to ensure the tubing is not attached to a moving part unless absolutely necessary.

Then, keeping the tube coiled as much as possible, I began by running the tubing down and back from the compressor using the frame as an attachment point where possible. Once I got to a cross member, I made every attempt possible to route the cable above the cross member rather than below it. This minimizes the possibility of trail damage. I also made every effort to securely attach the tubing in as many locations as possible, which on a Montero, is not that frequent. I did find a number of pressed in bolts where I could use a metric bolt and attach a wire strap to retain the tube.

Once I got to the rear differential, I lifted the rear of the vehicle from one tire, flexing the rear suspension. Once the suspension, was at it's maximum flex, I connected the tubing to the differential unit and secured everything so I wouldn't have loose hoses to catch on the trail. Once secured, I lower my Monty and raised it again to ensure the secured hoses had enough slack, but at the same time, not too much.

Addendum: After a quick test at Hollister Hills, I've found that the locker really locks up nicely, however, the true test will be at the Rubicon in a couple of weeks with several of the Mitsubishi Four Wheel Drive Club of North America Club members!!

Contacts: Related Links:
  • Ray Sala
  • ARB USAAir Locker Inc. 20 South Spokane Street, Seattle, Washington, USA

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