Geotab HRN-CX10S4 Harness: Fitment, Install and Specs

What Is the HRN-CX10S4?

The HRN-CX10S4 is an optional Geotab harness that adds starter inhibit to a Geotab Keyless installation, so the vehicle will not crank unless the IOX-KEYLESS allows it, and it is made for bladed-key vehicles running IOX-KEYLESS hardware version B1 or later with a GO9. It carries a standard automotive relay that our technicians splice into the vehicle's starter wire.

For shared fleets, that means a driver needs a valid Keyless booking to start the truck, not just a key. It is a theft and misuse control as much as a scheduling tool.

Harness sketch of the HRN-CX10S4: the 10-pin plug to the IOX-KEYLESS, the relay using its common and normally closed contacts, plus ignition and ground leads.

Which Vehicles and Devices Does the HRN-CX10S4 Work With?

Geotab's identification table lists this as a starter inhibit harness for Keyless on bladed-key installs. It needs an IOX-KEYLESS marked hardware version B1 or newer, paired with a GO9, and Geotab states that it must not be used on IOX-KEYLESS units without that label. On B1 units it takes the place of the older HRN-CX09Y5. The listed length is 160 cm (63 in), the connected maximum is 2 m (6.5 ft), and it is made in China.

Geotab's dedicated Keyless starter inhibit guide adds the electrical picture. The relay is a 12 V Form-C type, using common (30) and normally closed (87a), with the normally open contact (87) left unwired. Contacts are rated 30 A at 14 VDC, and the harness draws roughly 49 mA when operating at 12 V. Push-button start vehicles are excluded, and Geotab offers no starter inhibit guidance for hybrid or electric vehicles.

What Problem Does It Solve on the Job?

Motor pools, rental-style fleets and shared work vans all hit the same issue: keys get copied, borrowed and left in cup holders. With the HRN-CX10S4 fitted, a key alone no longer starts the vehicle. The driver books it in the Keyless app, checks in, and only then does the starter respond.

Because the relay rests closed, a dead GO device or a pulled connector leaves the vehicle startable. That protects the customer from stranding a crew because of an electronics fault.

How Is the HRN-CX10S4 Installed?

Geotab aims this work at partners and advanced certified installers with real-time wiring diagrams. Our sequence, based on Geotab's guide:

Collect the make, model, year and trim list ahead of the visit so diagrams can be pulled.
Confirm the IOX-KEYLESS label reads H/W: B1 or later.
With a digital voltmeter, find the wire that shows 12 or 24 V only with the key in START.
Cut it with slack on both ends. The black relay lead goes to the switch side, the white/black lead to the starter side. Solder and heat-shrink both.
Connect the fused yellow lead to a true ignition source, live in ON/RUN and START and dead in ACC and OFF, never to the battery or an ECU sense wire.
Ground the black lead to chassis metal, checking behind any drill point first.
Plug the 10-pin connector into the IOX-KEYLESS, then let the GO and IOX firmware update until all three LEDs go solid with ten beeps.
Run the relay test: starts with relay in; keeps running with relay pulled; will not start with relay out; starts again with relay back.
Finish with a Keyless app test: book, check in, start, check out, confirm no start.

Total harness length stays within 2 m (6.5 ft), no T-harness is ever joined to another, and every module is cable-tied in place.

In-vehicle sketch: the relay sits in the cut starter wire between key switch and starter, controlled by the IOX-KEYLESS on the GO9.

Spec	Detail
Part number	HRN-CX10S4
Function	Starter inhibit for Geotab Keyless, bladed-key vehicles
Requires	IOX-KEYLESS H/W B1 or newer, with GO9
Replaces	HRN-CX09Y5 on B1 IOX-KEYLESS
Status	Optional
Length	160 cm (63 in)
Relay	12 V Form-C, contacts 30 and 87a used, 30 A at 14 VDC
Not for	Push-button start; unlabelled IOX-KEYLESS

What Should You Watch for When Fitting It?

If the engine dies when the relay is pulled during the local test, the wrong wire was cut, so go back to the diagram. Vehicles with auto stop-start need extra thought, since an inhibit event must never leave a truck stalled in traffic. Some makes monitor starter circuit impedance or have their own inhibit interfaces and will throw codes if the wire is cut. Geotab asks for photos of the VIN, the soldered splices and the sealed wiring, and for ties roughly every 150 mm (6 in) along the run.

Which Related Harnesses Should You Compare?

HRN-SIFUSETAP: feeds a starter inhibit relay by tapping an existing fuse instead of only cutting wire.
SPR-RELAYKIT: a relay kit driven by driver ID or IOX-OUTPUTM rather than Keyless bookings.
HRN-INTX21ATC: an ATC fuse interrupter used with the fuse-tap method.

What Are Common Questions About the HRN-CX10S4?

Can the HRN-CX10S4 go on a push-button start vehicle?

No. Geotab limits starter inhibit with this harness to bladed-key starts, because Keyless already controls starting on push-button vehicles.

What if the IOX-KEYLESS label does not show H/W: B1?

Do not connect it. Geotab warns that earlier hardware can be damaged by this harness, so our technicians confirm the label first and sort out a compatible unit if it is not B1 or later.

Will the vehicle still start if the GO device loses power?

Yes. The relay contact used is normally closed, so if the GO device or harness loses power or is unplugged, the starter circuit closes and the vehicle starts as normal.

Starter inhibit is work for an experienced hand, and our team brings 35 years of twelve-volt wiring to it. We supply the Keyless parts and GO devices and install them at the customer's yard. Phone 803-513-1009 to talk it through, or request pricing on Get a Quote.

Sources: Geotab harness identification, HRN-CX10S4; Geotab Keyless starter inhibit guide for HRN-CX10S4. GEOTAB is a registered trademark of Geotab Inc. API Signal is an independent installer and is not Geotab.

Every Geotab Harness →All 83 harnesses and accessories by part number. Get a Quote →The HRN-CX10S4 supplied and installed on one written quote.

Geotab HRN-CX10S4 Harness