Geotab HRN-TNULL-A Harness

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What Is the HRN-TNULL-A?

The HRN-TNULL-A is a T-harness that connects a custom device, with a dash cam as Geotab's own example, to a GO device using the GO device's IOX port. Geotab's harness list sums it up as a T-harness for linking a GO device with a custom device, publishes a length of 120 cm (47 in), and lists it as TAA compliant and made in Mexico.

The Geotab Marketplace listing for the HRN-TNULL fills in how it works. It describes a T-harness that delivers power, ground and CAN lines to two outputs: a micro-MOLEX connector and a standard IOX connector. One branch feeds the custom device, and the other keeps the IOX chain open for further modules.

The point is to make dash cam installs simpler. Instead of running a separate power feed from the fuse panel to the dash cam, the device takes what it needs from the GO device's IOX port through the right adapter. Fewer splices into vehicle wiring means fewer places for a fault to start.

Which Vehicles and Devices Does the HRN-TNULL-A Work With?

Like other IOX-side parts, this harness is not tied to a vehicle make. Its compatibility questions are about devices. Geotab's Marketplace listing says the HRN-TNULL is for GO9 devices and is not intended for GO8 and earlier models. On the custom device side, it is listed as usable today with the Surfsight Power Harness, and Geotab says other Geotab-approved dash cam solutions can be powered using the dash cam maker's adapter cable.

So the harness is one piece of a three-part chain: the GO device, the HRN-TNULL-A, and a power harness or adapter that belongs to the dash cam. Ordering the T-harness alone is not enough to finish the job, which is why we confirm all three before booking.

What Problem Does It Solve on the Job?

Dash cam installs usually take more time on power than on mounting. A typical hardwire job means finding a constant and a switched circuit in the fuse panel, adding fuse taps and running wire up the pillar. Every one of those connections is another chance for a mistake, and on a large rollout, small inconsistencies add up.

Taking power from the GO device's IOX port standardizes that step. Geotab specifically pitches the harness as a way to avoid wiring into the vehicle fuse panel. Because the second branch keeps a standard IOX connector, a fleet that later adds driver ID or other IOX modules does not have to undo the dash cam install to do it.

How Is the HRN-TNULL-A Installed?

Geotab has not published a step-by-step guide for this harness. The sequence we follow uses Geotab's general IOX installation rules:

• Confirm the vehicle has a GO9-family device and that the dash cam's own power harness or adapter is on hand.
• Pull the GO device out of its vehicle connection and take the cover off its IOX expansion port.
• Connect the HRN-TNULL-A to the IOX port and tie the connection so vibration cannot work it loose.
• Join the micro-MOLEX branch to the dash cam's power harness, and route that cable up to the dash cam location behind trim, clear of airbag panels.
• Connect any other IOX modules to the standard IOX branch, or leave it capped and tied.
• Reconnect the GO device, start the vehicle, and confirm both the GO device on MyInstall and the dash cam's own power-up and connection.

Which Related Harnesses Should You Compare?

• HRN-IOXEXT-A: straight 2 m IOX extension with no split, for moving modules away from the GO device.
• HRN-UD03S9: 14 ft serial extension for the IOX-RS232D data link.
• HRN-SIFUSETAP: fuse tap harness, for jobs where power comes from the fuse panel instead.

What Are Common Questions About the HRN-TNULL-A?

Which GO devices work with the HRN-TNULL harness?

Geotab's Marketplace listing for the HRN-TNULL says it is for GO9 devices and is not meant for GO8 or earlier units. We confirm the device generation in the vehicle before planning a dash cam install around it.

Does the HRN-TNULL-A power a dash cam on its own?

Not directly. Geotab describes it powering specific dash cam solutions when combined with that maker's power harness, such as the Surfsight Power Harness, or another approved system's adapter cable.

Can other IOX modules still be added?

Yes. The harness keeps a standard IOX connector on the branch, and Geotab notes that additional IOX devices can connect through it for further expansion.

API Signal supplies and installs Geotab harnesses and devices on site at the customer's yard, along with dash cams and backup cameras. Call 803-513-1009 or use Get a Quote to plan a combined telematics and dash cam install.

Sources: Geotab Harness Identification and Application, Geotab Marketplace HRN-TNULL, Geotab IOX-RS232 support document. GEOTAB is a registered trademark of Geotab Inc. API Signal is an independent installer and is not Geotab.