So you want to put an ARB compressor in a 1st gen

Hello again TW, I'm back with what I hope is some more information about a topic that I didn't find a ton of information about - mounting an ARB compressor into the 1st gen's relatively tight engine bay (granted, I am a newer member, so I may just suck at using the search function).

The twist to my particular situation is that I had already installed an accessory relay/fuse panel, and I wanted to integrate my compressor seamlessly into that rather than using ARB's wiring harness. So, this post will provide instructions on 1) how/where to jam the ARB compressor under the hood, 2) how to tie in to an accessory panel, and 3) how to install an elegant and clean illuminated rocker switch for your compressor into the dash panel of your truck.

NOTE: I never plan on running air lockers off of my compressor, so this solution worked for me. If you ever want to run lockers, you'll need to either use the ARB harness, or figure out the more complicated custom wiring job that you would need to do to tie in to an accessory panel.

Part 1: Mounting the compressor

Some previous posts that I found in this forum mentioned mounting the compressor to the passenger side of the engine bay, to the rear of the air filter. The left composite image below shows a solution that TW member betterbuckleup found. On the right, you can see that isn't an option if your truck is equipped with ABS, since the controller occupies that spot. AventureTaco found another solution that involved mounting to the firewall, but I wasn't mega stoked about having the modify the cowl.



With some finagling and minor (temporary) disassembly of the air intake, I was able to make the location below work (final assembly shown). I believe this location should work regardless of how your truck is equipped.



Try various orientations of the compressor and confirm that it fits the pictured location prior to disassembly. Once it fits, secure it in that orientation and then remove the filter box to give you enough access to work in this area. Additionally, you'll need to remove the intake elbow temporarily in the engine bay, and the plastic tube from the passenger wheel well. A photo of the removed intake is shown for reference, but there's a good thread detailing how to do that here as part of the "elbow delete" mod, which you might choose to do: https://www.tacomaworld.com/threads/intake-in-fender.2799/



Once you have the filter box and tubing removed, it's pretty easy to line up the ARB template and drill holes from the engine bay side (I'm documenting this work after the fact, so I don't have any photographs of this step). Make sure you've removed the intake tube before drilling, or you will drill holes into it! The rest of the installation is pretty simple, insert the provided carriage bolts from the compressor side and install the provided nuts on the wheel well side. You'll need to dremel off the excess threads to provide clearance to get the intake tube back in the truck. Reinstalling the filter box and elbow is tight, but can be done with patience. This setup does not interfere with your ability to use the clamps holding the lid on the filter box.

 

Part 2: Modifying Output Tee

With the compressor installed, the next problem that I had was with the tee that ARB provides to allow you to connect both the air chuck and the high-pressure kill switch to the compressor output. The male section of this tee threads into the compressor output.



If you look at the image of my mounted compressor above, you'll see that using this tee will result in a collision of either the air chuck or the pressure switch with the closing hood. Not good! I located a brass inline tee, 1/4" NPT Female x Male (P/N 50785K322 from McMaster) to keep everything under hood level.

 

Step 3: Underhood Wiring - Prep and Selection

The next step of the project was to throw away 99% of the ARB wiring harness. The only piece that I saved was the male fitting that plugs into the compressor power itself, since I could not locate this part anywhere. I cut it off and saved enough wire on the end to add butt connectors later.



I now had to decide on the wiring size. The ARB technical specs for the

$322 CKMA12 On-Board Air Compressor High Performance 12 Volt for Air Locker Differentials and Tire Inflation

CKMA12 specify 32 amps under maximum load (100 PSI) at 12 volts, per the table below.



My Bussmann panel was located on the other side of the engine bay, so I figured a run of about 5' (one way to load) was all that was needed. Consulting the chart for the U.S. Coast Guard marine wiring standard showed that my proper wiring size for a critical (3%) voltage drop for 5' one-way @ 40 amps (next size up) is 8 AWG. I never intend to run the compressor to full load, and the Bussmann panel I have uses Metri-Pack 280 connectors, which are limited to a maximum of 10 AWG. So, I selected 10 AWG, with the intention of fusing the circuit for 30 amps and adding in a pressure switch with a lower setpoint (60 PSI or so). I'm not an electrician, so maybe somebody who is can weigh in as to how sketchy this is.

 

Step 4: Underhood Wiring - "Theory"

This next post assumes you've built and installed a Bussmann panel for your truck following this EXCELLENT thread. You'll recall that up to six wires are passed through the firewall to be used as your cab-side harness (five switch wires plus ground). These wires can be connected to switches in the cabin to control the relays in your panel. Since the ARB compressor is a high-current accessory, it makes sense to switch power to it via one of the 35 amp relay circuits in your Bussmann. It would be easy enough to just wire in a switch in the cabin, wire the compressor under the hood, pop in a fuse and call it a day, except for one problem - the pressure switch won't work, and you'll potentially blow up the compressor:



You'll need to modify your Bussmann a bit for this accessory. In the image above, you feed your cabin rocker switch with 12 volts from a fuse tap take-off in the cabin fuse box, route the return wire through the firewall, and connect to your relay coil through pin 86 on your RTMR. Instead, include the pressure switch in series with your cabin rocker switch per the diagram below. With this configuration, both the cabin rocker and the pressure switch must be closed (i.e. compressor output less than switch cutoff pressure) before the compressor relay is energized.



If you have illuminated switches like the OTR rocker pictured above, you'll also need to tap into your dash dimmer circuit, which is a topic covered here (see the end of post #6).

 

Definitely saving this for later

 

Thanks! I love doing write-ups like this. Hope it helps you down the road!

 

Step 5: Just Show Me the Friggin' Results

Ok, let's finish this by doing some wiring. Select a rocker switch. There's tons of options available; I used this sweet OTRATTW SPST rocker. Choose where you want to mount the switch in your truck. There's several options, just make sure to measure before ordering your switch. I selected the circled area (next to dash dimmer) in mine, which was covered with a switch blank. I did have to very slightly enlarge the edges of the cutout (a dremel worked well), after which the switch snapped in.



Next, I supplied the switch with 12 volt power from a fuse tap in my cabin fuse box. Select a fuse that has power when the ignition is ON (I chose the accessory fuse in slot #2). Wire up the switch to the harness from your Bussmann panel. If you want a dimmable switch, follow the instructions in the thread I mentioned earlier. Fuse the new circuit with 5 amp low profile fuse.



Back under the hood, I used 10 AWG TXL primary wire to wire the compressor, and 18 AWG TXL primary wire for the run from the rocker in the cabin to the pressure switch. These wires were loomed together in 1/2" slit loom, and the loom secured to the firewall with adhesive-backed cable holders, all from McMaster. The previously-mentioned connector that I cut off of the ARB harness was joined to the new run with butt connectors; Metri-Pack connectors were used to make the connection to the Bussmann.



The final step was to insert a 30 amp fuse and 35 amp relay into the Bussmann panel.



I've omitted some minor details, but the major steps to do this install are all here! All that's left to do is enjoy your new onboard air. Hope you found this guide to be helpful!

 

Damn this is a great write up! Cheers to you.
Gotta love the Carl pics too..