On a heavy truck the device gets plugged into a 9-pin harness and then it has to live somewhere. Put it on a Y-split and it goes up behind the dash, out of the way, with the port still open for a dealer scan tool. Skip the Y-split and it ends up on the floor.
The short answer
- Without a Y-split: the harness hangs out of the port and the device sits at the side or on the floor.
- With a Y-split: the device is mounted up behind the dash and the port stays open.
- Same device either way. What changes is where it lives.
- Already know you need one? It is on the Install Parts page.
What goes wrong without one
A 9-pin device comes off the port on a harness, and unless somebody mounts it properly, that harness and that device end up loose in the cab.
- The device sits on the floor or wedged down beside the seat, where it gets stood on, kicked and soaked.
- Slack harness everywhere. Loose cable in a footwell is something to catch a boot on.
- The port is occupied. Nothing else can plug in while the device is in there.
- Anyone can pull it out in seconds, and there is nothing to show for it afterward.
The port has to stay free for the dealer
This is the part that costs the most on a heavy truck, because these vehicles get scanned constantly.
- A dealer scan tool cannot get in while a device is sitting in the port.
- Somebody unplugs it to do the work — and quite often nobody plugs it back in.
- You find out days later, when the truck has been dark on the map and nobody said anything.
- A Y-split passes the connection straight through, so the scan tool plugs in with the tracker still connected.
What a Y-split changes
- The device goes up behind the dash instead of on the floor. Out of the wet, out of the way, out of reach.
- Higher is better for the signal too. More sky above it means a tighter fix and fewer gaps in the trail.
- The harness is routed and secured, not left in a heap.
- Nothing is cut and nothing is spliced. The factory wiring is untouched, which matters at trade-in.
- It comes out as cleanly as it went in, so it can move to the next truck.
One kit instead of a part number per truck
This is what saves the most time on a rollout. Rather than matching a harness to every make and model in the yard, a universal kit carries the adapters with it.
- Our 9-pin J-series harness fits all 9-pin trucks — old or new, black or green. No part-number matching truck by truck.
- The Geotab HRN-GS09K2-A kit ships with four numbered mounting adapters, so the vehicle does not have to be known in advance.
- On a mixed fleet that is one line on the order instead of a spreadsheet of part numbers.
- A truck that turns up unexpectedly does not stop the day.
Get the harness. The Geotab HRN-GS09K2-A 9-pin heavy-duty T-harness kit is on the parts page, in stock, with shipping at $12.99 for the first item and $1.00 for each additional item.
Shop Install Parts
Is it definitely a 9-pin?
Worth thirty seconds under the dash before you order. It takes a look, not a tool.
- 9-pin J1939 — round, with a threaded locking ring. Heavy trucks.
- 6-pin J1708 — round and older, still on plenty of working equipment.
- Green or black does not matter for what you order from us. Our harness fits both.
Look under the dash on the driver’s side, usually near the kick panel or the steering column. If you are not sure, photograph the port and email it to info@apisignalcorp.com.
What the year usually tells you
- 1996 to 2001: generally 6-pin J1708.
- 2002 to 2006: could be either — check the truck, do not assume.
- 2007 onward: almost always 9-pin J1939.
- A mixed-age fleet is normal, so expect more than one connector type in the van.
What about RP1226?
Newer trucks increasingly carry an RP1226 connector, a 14-pin accessory port put there specifically so telematics and other add-on devices have somewhere to go.
- It is designed for exactly this. Fitting a device there leaves the diagnostic port completely alone.
- It is not on every truck yet, so plan for 9-pin as well rather than instead.
- Some makes route it differently — a photo of the port area settles it faster than a spec sheet.
Older equipment on 6-pin
- 6-pin J1708 is still out there on plenty of working trucks and yard equipment.
- It is not a lesser install — it just needs the right harness, and those exist.
- Do not retire a truck from your tracking plan because it has an older port. If it runs, it can be tracked.
Frequently asked
Why does a heavy truck need a Y-split harness?
Because the device comes off the port on a harness and has to live somewhere. A Y-split lets it be mounted up behind the dash instead of on the floor, and passes the diagnostic connection through so a dealer scan tool can still plug in.
Do I need a different harness for a green connector than a black one?
No. Our 9-pin harness fits all 9-pin trucks, old or new, black or green.
Will one 9-pin harness fit my whole fleet?
If the trucks are 9-pin, yes. The Geotab kit also ships with four numbered mounting adapters, so the vehicle does not need to be identified in advance.
Rather have us do it? We install GPS, cameras and telematics across Georgia, South Carolina and North Carolina, at your yard. Get a free quote.
This information is provided as a guide. Verify every circuit with a digital multimeter before connecting to it. Proper installation is the responsibility of the installer.
