Mastering Geotab
★ Geotab Harnesses · Make-Specific and Custom Harnesses
The HRN-FUEL3W is Geotab's fuel gauge tap-in harness for three-wire installations, where the GO device is wired to ground, ignition and constant power instead of plugging into a diagnostic port, plus a lead for the fuel sender signal.
The HRN-FUEL3W is a Geotab harness that powers a GO device by the three-wire method (ground, ignition and constant battery feed) and also taps the analog fuel level signal, so a vehicle with no usable diagnostic connection can still report tank level. Geotab lists it as the fuel gauge tap-in harness for three-wire applications.
Three-wire installs exist for vehicles where a diagnostic port harness is not the right answer: older or simpler chassis, specialty bodies, or units where the port is unsupported. Until this harness, those vehicles gave GPS and trips but no fuel picture. The HRN-FUEL3W adds that missing number.
On Geotab's identification table, the HRN-FUEL3W is described as a fuel gauge tap-in for three-wire applications, 75 cm (29.5 in) long, made in China. The table does not name a required base harness or a part it replaces, which fits its job: it is the power harness and the fuel input in one.
Vehicle support comes from the same fuel harness vehicle list that governs the HRN-FUEL. The models on it today are Asia-Pacific market trucks and pickups such as the Isuzu N-series, Hino Dutro 300 series and Toyota Hilux, with a note that data availability changes with build year and market. Because the list does not yet include models built for the North American market, we review each chassis against it before committing to a fuel install, and where a vehicle is missing, Geotab accepts a model support request that we can lodge on the customer's behalf.
Hard-wired installs are common on equipment and older trucks that fleets keep for years because they still work. Those are often the vehicles with the least data, and the ones where fuel goes missing without anyone noticing. Giving them a tank level reading lets a manager compare refuel receipts against actual level changes, flag a level drop while parked, and plan fuel deliveries for vehicles that rarely visit a station.
It also saves a second harness. Rather than one harness for power and another for the fuel signal, a single part does both, which means fewer joints to fail behind the dash.
Geotab's Isuzu N-series guide carries a three-wire branch, and our technicians follow its logic on supported vehicles:
The diagnostic port steps in that guide are skipped for a three-wire job. Geotab's 2 m (6.5 ft) maximum on total harness length still applies, as does its rule against chaining T-harnesses.
| Spec | Detail |
|---|---|
| Part number | HRN-FUEL3W |
| Origin | China |
| Application | Fuel gauge tap-in for three-wire installs |
| Length | 75 cm (29.5 in) |
| Power wiring | Red to constant battery with 5 A fuse; yellow to ignition with 5 A fuse; black to chassis ground |
| Fuel input | Green ANALOG FUEL lead to sender signal wire |
| Vehicle support | Geotab fuel harness vehicle list (shared with HRN-FUEL) |
An accessory circuit is not ignition. If the yellow lead lands on a feed that drops out during cranking or stays live with the key off, trips will be wrong and the battery can suffer, so prove the source with a meter in every key position. Never skip the inline fuses. Pick a ground on bare chassis metal, not a painted bracket. Expect wire colors on the vehicle to differ from Geotab's example truck, and confirm the sender wire against the specific guide rather than guessing from color alone.
The HRN-FUEL rides inside an OBD-II T-harness setup with the HRN-GS16K22-A. The HRN-FUEL3W is for three-wire installs, where the GO device takes power, ignition and ground from hard-wired connections and no diagnostic port harness is used.
Geotab's three-wire instructions call for a 5 A fuse on the red constant power wire and a 5 A fuse on the yellow ignition wire.
A three-wire install does not use the diagnostic port, so the GO device does not read engine data through it. The harness adds the fuel gauge signal alongside GPS and ignition-based trip data.
Hard-wired jobs are where 35 years of twelve-volt experience earns its keep. API Signal provides the Geotab harnesses and devices and installs them on site at the customer's yard, so equipment stays where it works. Ring 803-513-1009, or describe the units on our Get a Quote page.
Sources: Geotab harness identification, HRN-FUEL3W; Geotab Isuzu N-series fuel harness guide (three-wire section); Geotab fuel harness vehicle list. GEOTAB is a registered trademark of Geotab Inc. API Signal is an independent installer and is not Geotab.
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