Wire an ARB Compressor in Your INEOS Grenadier: 40A Guide

The Short Answer

To wire an ARB compressor in your INEOS Grenadier, you have three options: tap the factory 40A compressor pre-wire (non-US, high-load spec only), run direct to the battery with proper fusing, or use a DTP roof port via an Anderson adapter for lower-draw portable units. On factory-pre-wired Grenadiers, the brown wire under the rear seat is your +12V live feed — connect your ARB relay here. Do not use the yellow (ignition-switched) wire to power the motor; it cannot handle the 32A+ draw of an ARB compressor.

Why ARB Compressor Wiring Trips Up Grenadier Owners

The INEOS Grenadier looks like a simple 12V wiring job until you get under the seat and find three wires — brown, yellow, and black — and no documentation explaining which one is safe to use. Every forum thread on this topic starts with the same question: "Do I connect to the brown or the yellow?" The answer matters because the yellow ignition-switched wire is not rated for compressor motor current, and wiring to it can cause intermittent failures or damage the switched circuit.

There's also a market split that catches US buyers off guard. Non-US and high-load-spec Grenadiers include a dedicated 40A compressor pre-wire run from the interior electrical centre to under the rear seats. US-market standard Grenadiers do not have this circuit — power has to come from the battery or busbar directly.

Option 1: Factory 40A Compressor Circuit (Non-US, High-Load Spec)

If your Grenadier was spec'd with the high-load electrical package or delivered outside North America, you likely have a factory compressor pre-wire already run to the underside of the rear seats. This is the cleanest and most purpose-built install path.

Identifying the Circuit

Look for the three-wire harness under the rear seat in the driver-side compartment. The wires are:

• Brown: +12V permanently live, sourced from the starter battery through fuse FI13 in the interior electrical centre. This is your motor power feed — rated 40A.
• Yellow: +12V ignition-switched. This circuit is not rated for motor operating current (32A+). Use it only as a relay trigger if you want the compressor to power off with the ignition.
• Black: Earth/ground. Connect to the body earth point adjacent to the 40A connection, or directly to a nearby chassis lug.

Forum member clark-kent, who worked through this wiring in detail in February 2026, confirmed the wire roles after testing fuse FI13:

"This circuit is fused at FI13 in the interior electrical centre behind the starter battery. I'm using the yellow wire to operate the NATO socket contactor so the NATO socket is live whenever the ignition is on. The yellow ignition switched wire does not look suitable to power your compressor which can draw 32amps. You can use the switch on your compressor to turn it on and off." — clark-kent, TheIneosForum, "Wiring question for mounting ARB CKMP12 compressor," Feb 2026

Wiring Steps (Factory Circuit)

1. Locate the brown/yellow/black harness under the rear seat, driver side.
2. Connect your ARB relay's main +12V input (thick red wire, or battery positive on the relay module) to the brown wire.
3. Connect the relay ground (black) to the black wire or body earth point.
4. If you want ignition-dependent operation: wire the relay trigger input to the yellow wire. The relay coil draws only ~200mA, which the yellow wire handles fine — it's only the motor current it can't carry.
5. Keep your ARB inline fuses intact. If there's a fuse holder on the cable to the compressor motor, leave it in place.
6. Route the compressor output (air hose) to your chosen outlet position.

Another Grenadier owner confirmed the same wiring in the fixed-air-compressor forum thread (2023):

"I took the power from the INEOS supplied wires in the same compartment (brown - permanently live, black - negative/ground). They are connected to a 40amp fuse (F113 from memory) and so will draw power from the starter battery. I connected the brown and black to the ARB relay." — TheIneosForum, "Fixed air compressor," Jun 2023

Option 2: Direct to Battery (US Market + All Markets)

US-market Grenadiers do not have the 40A pre-wire. Even on non-US vehicles, many owners skip the pre-wire and go direct to the battery for simplicity or to support twin-motor setups that need 60–80A capacity. This is the recommended method when running an ARB CKMTP12 twin compressor.

Fusing Strategy

For the twin ARB CKMTP12 (up to 32A combined), the correct fusing hierarchy is:

• Main feed fuse: 80A between battery positive and your compressor power distribution point. Mount this as close to the battery as possible.
• Per-motor protection: Keep the 40A inline fuses that come with the ARB wiring harness — one per motor. These protect the individual motor circuits.

Forum member lwa55dal documented this approach when installing the twin-compressor bracket kit in September 2024:

"I am planning to install the main power on the 5th post of the Littlefuse busbar with an 80 amp fuse, but I am going to leave the single 40 amps in the wiring harness in-line as they protect each compressor." — lwa55dal, TheIneosForum, "Wiring ARB twin compressor," Sep 2024

Another owner confirmed the same approach, using a spare 80A lug on the fuse block adjacent to the starter battery:

"Next to and slightly behind the starting battery, inboard, on the passenger side, I had a spare 80amp space here with plenty of spare empty lugs on the floorboard for ground. Perfect!" — TheIneosForum, "Wiring ARB twin compressor," Sep 2024

Wiring Steps (Direct to Battery)

1. Run your main feed cable (6 AWG minimum for the twin, 8 AWG acceptable for single) from the battery positive terminal.
2. Install an 80A ANL or blade fuse within 12 inches of the battery.
3. Route to the compressor location (under seat, under bonnet, or rear compartment).
4. Connect to the ARB relay module's main +12V input.
5. Ground the relay and compressor frame to a chassis bolt. The Grenadier has multiple M8 chassis lug points near the battery area — use any that are already grounded.
6. Connect the relay trigger wire to your chosen switch source: ARB's included switch, a Grenadier AUX switch (via the fuse block), or direct ignition-switched power.

Option 3: DTP Roof Port (Portable Compressors, Lower Draw)

The Grenadier's factory DTP-06-2S roof ports deliver switched 12V power rated up to approximately 20–25A per port. This is not enough to run an ARB CKMTP12 twin under load, but it works well for:

• ARB CKMP12 single compressor at light-duty cycles (inflate tires from 25 to 35 PSI on a 30L tire — draws ~17A)
• Smaller portable compressors (12–15A max draw)
• Situations where you want completely plug-in, no-drill power with the accessories switch active

The DTP port is switched with the Grenadier's accessories, so the compressor is off when the vehicle is off — no accidentally draining the battery with a forgotten-on compressor. DVA's DTP-06-2S to Anderson SB50 cable connects the roof port directly to any Anderson-connectorized compressor in a fully reversible, no-drill setup.

ARB Relay Wiring Explained

ARB compressors (CKMP12, CKMTP12) include a relay module in the wiring harness. Here's how it maps to the Grenadier circuits:

On the ARB switch, when the connector block is facing you: top left = black (ground), middle = red, bottom = purple. Confirmed by multiple owners during the bracket kit thread in September 2024.

Mount Positions in the Grenadier

Three proven locations for ARB compressor mounts on the Grenadier:

Under the Rear Seat (Most Common)

The driver-side under-seat compartment is the most popular location. Purpose-built under-seat compressor mounts fit here — both single and twin configurations are available. The factory 40A pre-wire harness (non-US) terminates nearby, and there's space for the air line to exit toward the rear cargo area. Ventilation can be a concern — ensure the mounting position doesn't trap heat around the motor.

Under the Front Seat

Purpose-built twin-compressor front-seat mounts are available for the Grenadier. This positions the compressor close to the battery for shorter wiring runs and uses the busbar fuse block nearby. Confirmed working by multiple US-market owners who don't have the 40A pre-wire.

Under the Bonnet (Tight, Possible)

Space under the Grenadier bonnet is limited, but a single ARB CKMA12 can fit in the area forward of the wheel arch guard. The ARB CKMTP12 twin is too large. Ventilation is better under the bonnet, but longer hose runs are needed to reach the rear of the vehicle.

Troubleshooting

Compressor Runs But Cuts Out

Check fuse FI13 (factory circuit) or your inline 40A fuses. The ARB thermal protection will also cut out the compressor if it overheats — allow 15 minutes to cool before retrying. Running at sustained high pressure (airing down from highway to off-road) taxes the motor harder than standard tire inflation.

Switch Light On But No Air

On the ARB switch: black (top left), red (middle), purple (bottom). Swapped red and purple will light the switch but not trigger the relay. Verify the switch orientation as described above.

Compressor Stays On After Ignition Off

If you wired directly to the brown (always-live) wire without using the yellow trigger through a relay: the compressor relies entirely on your ARB switch to turn off. This is normal and safe — just remember to turn off the compressor switch before leaving the vehicle.

US Market: No Wires Under Rear Seat

Correct — no factory 40A pre-wire on US-spec Grenadiers. Proceed with Option 2 (direct to battery). Use the fuse block adjacent to the starter battery as the power source, not the rear seat harness.

DVA Power Solutions for Grenadier Compressor Wiring

DVA makes two products that simplify compressor power connections from the Grenadier's factory DTP system:

• DTP-06-2S to Anderson SB50 Cable (3m) — Routes power from the factory roof DTP port to any Anderson SB50 connector. Plug-and-play for portable ARB compressors or any Anderson-terminated 12V device. No drilling, no permanent wiring.
• DTP-06-2S to IP65 Waterproof Splitter — Splits one roof DTP port into two weatherproof outputs, useful when you want to run a compressor and a fridge from the same roof port circuit.
• PowerVault™ Utility Hub R2 — Mounts in the Grenadier's exterior utility space and provides multiple switched 12V outputs including Anderson SB50 sockets — ideal if you want a permanent, exterior-accessible compressor connection without running wires through the interior.

Browse the full DVA Power & Connectivity collection for the complete range of DTP adapters, splitters, and power distribution solutions.

Frequently Asked Questions

Which ARB compressor fits best in the INEOS Grenadier?

The ARB CKMP12 (single motor) fits under the rear seat and under the bonnet. The ARB CKMTP12 twin fits under the rear seat with a purpose-built under-seat mount or under the front seat with a purpose-built front-seat mount. The twin is the better choice if you run air lockers — it handles simultaneous locker engagement and tire inflation without the single motor's extended duty cycle.

Can I use the Grenadier's AUX switch to control the ARB compressor?

Yes. The Grenadier's factory AUX 1–4 switches send a switched +12V signal to the relay when activated. Wire the ARB relay trigger (thin red wire) to the AUX output pin for a clean, dash-controlled compressor that integrates with the factory switch panel. You'll still need a separate main power feed for the motor circuit.

What gauge wire do I need for ARB compressor wiring?

For the ARB CKMP12 single (~17A): 10 AWG minimum for the main feed. For the CKMTP12 twin (~32A): 6 AWG for the main feed, 10 AWG for each motor branch. The ARB-supplied wiring harness may use 8 AWG — check before relying on it for the full run from battery to compressor.

Does the factory 40A circuit draw from the starter battery or aux battery?

The factory 40A pre-wire (non-US models) draws from the starter battery through fuse FI13. Always run the engine when using the compressor for sustained periods to avoid draining the starter battery.