Mastering Geotab
★ Geotab Harnesses · Make-Specific and Custom Harnesses
The HRN-CG13S1-A is a short Geotab adapter that sits between a universal 16-pin T-harness and the GO device to strip power transients off Pin 1. Geotab calls for it on every 24 volt vehicle and on 12 volt Volvo and Mack engine vehicles.
The HRN-CG13S1-A is a 10 cm (4 in) inline adapter that protects a Geotab GO device from power transients on Pin 1 when the device is fitted to a 16-pin universal harness. Geotab's own install guide calls it the SWC adapter and states it must be installed on 12 volt vehicles with Volvo or Mack engines and on all 24 volt vehicles.
It is a small part with a single job. On some trucks, the factory diagnostic port carries power or signal on Pin 1, and Geotab warns that transients there can damage the GO device's SWC chip. The adapter removes anything on Pin 1 from reaching the device. That makes it cheap insurance on a heavy-duty install that would otherwise use a universal harness built with lighter vehicles in mind.
Geotab designed it for the HRN-GS16K2 and HRN-GS16K22-A universal OBD-II harness kits. In its harness listing for the HRN-GS16K22-A, Geotab makes the adapter mandatory on all 24 volt vehicles and on 12 volt vehicles with Volvo or Mack engines, citing a known interoperability issue. That covers many buses and heavy trucks that present a 16-pin port.
The rule does not apply to every heavy-duty harness. Geotab states that the HRN-GS16K2-HD, its 24 volt heavy-duty T-harness, does not need the adapter. Geotab's install notes also advise using a vehicle-specific harness on heavy trucks whenever one exists, and falling back to this adapter on a 16-pin install when it does not. For North American Volvo and Mack trucks, those notes list both routes: the HRN-CE10K2 kit with the HRN-CM24Y1-A, or the universal HRN-GS16K22-A with this adapter.
Geotab publishes a separate product advisory, dated December 2024, covering the 24 volt and 12 volt Volvo and Mack adapter, and our technicians check that document before each job.
Think about a transit operator with a mix of 24 volt buses and a few 12 volt trucks running Volvo engines. The universal T-harness looks like the obvious, inexpensive way to cover all of them. Without the adapter, though, the device on those vehicles is exposed to Pin 1 transients that Geotab says can damage the GO unit. A failed device means a truck off the map, a return visit and a swap.
Fitting the adapter at the original install avoids that whole cycle. It also gives the fleet one consistent setup to document: universal harness, adapter, device. Geotab also tells 12 and 24 volt customers upgrading past GO8-era hardware to swap in an approved cable harness, and this adapter is part of that discussion.
Geotab's guide for the adapter is short, and the work fits inside a normal universal harness install:
| Spec | Detail |
|---|---|
| Part number | HRN-CG13S1-A |
| Geotab guide name | SWC adapter |
| Purpose | Removes the power transient on Pin 1 from the vehicle interface |
| Used with | HRN-GS16K2 and HRN-GS16K22-A universal 16-pin harness kits |
| Required on | All 24 V vehicles; 12 V vehicles with Volvo or Mack engines |
| Not needed with | HRN-GS16K2-HD |
| Length | 10 cm (4 in) |
| Harness run limit | 2 m (6.5 ft) total |
| Made in | China |
Do not decide by vehicle size alone. A 12 volt medium-duty truck with a Volvo or Mack engine needs the adapter, while a 24 volt bus on the HRN-GS16K2-HD does not. Check the engine plate and the system voltage before the van is loaded. The adapter adds a joint, so tie it close to the device to stop the two connectors from working loose on rough roads. If a GO unit on one of these vehicles has already failed, we look for a missing adapter before blaming the replacement unit.
No. Geotab says the HRN-GS16K2-HD heavy-duty T-harness does not need this adapter. It is the universal HRN-GS16K22-A and HRN-GS16K2 kits that call for it on 24 volt vehicles.
It plugs in between the universal 16-pin harness and the GO device, so the device connects to the adapter rather than straight to the harness.
Geotab warns that power transients on Pin 1 can damage the SWC chip inside the GO device on some 12 and 24 volt vehicles, and the adapter is its recommended protection against that.
Buses, tractors and mixed-voltage fleets are routine for our crews. API Signal checks voltage and engine make on every unit, brings the adapter where it is needed and fits the whole kit on site at your yard. Speak with us on 803-513-1009, or send your voltage mix through Get a Quote.
Sources: Geotab Harness Identification and Application, Geotab HRN-CG13S1-A SWC adapter guide, Geotab product advisory, 24V and 12V vehicle harness, Geotab specific install notes. GEOTAB is a registered trademark of Geotab Inc. API Signal is an independent installer and is not Geotab.
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