In short: If the tractor already has an ISOBUS display, use it: plug the implement into the rear ISOBUS socket and its screen appears there. Add a universal terminal when you want a second screen, when the tractor's display is too old or lacks AUX-N, or when the tractor has no ISOBUS at all. In that last case the tractor also needs ISOBUS sockets and a harness.
An ISOBUS implement runs on an ISOBUS terminal in the cab. Does the tractor's own display do that job, or do you need a terminal of your own? If you buy one, you need to know which, and what it will do once it is bolted into the cab.
Below: when the built-in screen is enough, how the common universal terminals compare, what a retrofit on a tractor without ISOBUS involves, and what to check before you pay for one.
What an ISOBUS terminal is
An ISOBUS terminal is the screen in the cab that shows the implement's controls. It comes in two forms. On most current ISOBUS tractors it is the tractor's own display, running the ISOBUS Universal Terminal (UT) function alongside the tractor's menus. The alternative is an aftermarket universal terminal: a separate screen that plugs into the tractor's in-cab ISOBUS socket and does the same job.
Either way, the principle is the same. The implement sends its own screen layout over the bus, and the terminal draws it. The terminal does not need to know the implement in advance, which is why a sprayer from one brand shows up on a tractor from another. The protocol side (object pools, soft keys, VT versions) is covered in ISOBUS Virtual Terminal Explained.
Tractor screen vs universal terminal
When the built-in screen is enough
If the tractor already has an ISOBUS display, start there. Plug the implement into the rear ISOBUS socket, and its screen appears on the display you already use. Most mid-range and larger tractors sold in the last decade or so ship this way, under their own brand names: Fendt Varioterminal, John Deere CommandCenter, Case IH AFS Pro, CLAAS CEBIS or CEMIS, Valtra SmartTouch and so on. The ISOBUS compatibility guide goes brand by brand.
The built-in screen is enough when it shows the implement, you can reach its controls without a second screen, and the tractor offers the extras you need (AUX-N, Task Controller). If the implement does not appear at all, work through the ISOBUS not working checklist before buying new hardware.
When you add a universal terminal
A separate universal terminal earns its place in three cases:
- You want a second screen. The tractor display runs guidance and tractor settings. The terminal next to it runs the implement full-time, so you are not swapping views at every headland.
- The tractor's screen is too old or too limited. An early display may lack AUX-N or Task Controller, or show modern implement screens poorly.
- The tractor has no ISOBUS at all. Then the terminal is only half the job. The tractor also needs ISOBUS sockets and wiring (see the retrofit section below). Whether that spend makes sense on a smaller farm is covered in is ISOBUS worth it on a small farm.
There is also a fleet argument. Move one terminal between tractors and the operator sees the same screen on every machine. Most universal terminals are sold with that in mind.
Universal ISOBUS terminals compared
These are the aftermarket universal terminal brands buyers ask about most: CCI, Müller-Elektronik, Topcon, Reichhardt, Trimble and Ag Leader. Tractor built-ins (Fendt, Deere, CNH and others) are not in the list; they come with the tractor. Model ranges and licence bundles change often, and many functions are sold as licences you unlock. So check the unit you are actually offered, on its current spec sheet, on four points:
| On the spec sheet | What to look for |
|---|---|
| UT version | Which Universal Terminal version the current software runs. Check it against what the implement maker lists. |
| AUX-N | Listed, and active on the unit you are offered, not a licence you still have to buy. |
| Task Controller | Which functions are licensed (TC-BAS, TC-GEO, TC-SC) and which cost extra. |
| Screen size | A compact screen that sits beside the main display, or a large one that shows two implements at once. |
Some of these brands also sell ISOBUS joysticks. A joystick is not a terminal. It plugs into the in-cab socket and works as an AUX-N input device next to whichever terminal you run. More on that under "What to check before buying".
Before you buy, check the terminal maker's compatibility list and the implement maker's spec sheet for the exact terminal and software version you will run. They tell you more than any brochure.
Retrofitting an ISOBUS terminal to a tractor without ISOBUS
A tractor with no ISOBUS needs more than a screen. A typical tractor retrofit kit contains:
- The terminal, with a cab mount.
- An in-cab ISOBUS socket, where the terminal (and any other in-cab ISOBUS device) plugs in.
- A rear ISOBUS socket, the 9-pin implement connector defined in ISO 11783-2, mounted at the back of the tractor for the implement to plug into.
- The harness between them, including the power feed from the tractor battery and the bus termination the network needs to work.
Reichhardt sells a kit of this kind: a rear plug, an in-cab plug and a harness with the termination built in. Other terminal makers and dealers sell their own versions. Pin by pin, both sockets are laid out in the ISOBUS connector pinout guide.
Who installs it? The kit is sold as bolt-on, but the job involves a battery feed, a cable run through the cab and a socket on the rear of the tractor. Most buyers have the dealer or an agricultural electrician fit it. If you are comfortable with tractor wiring, it is within reach. Either way, ask the tractor dealer first whether aftermarket ISOBUS affects the warranty.
Keep the two kinds of retrofit apart. This section is about the tractor side: giving a non-ISOBUS tractor a screen and sockets. If the tractor already has ISOBUS and the implement is the one without it, that is the opposite job, covered in the ISOBUS retrofit guide.
What the terminal will run once it is fitted
Once the terminal is in, it runs two kinds of things.
ISOBUS implements with their own ECU. A sprayer, spreader, seed drill or baler built for ISOBUS carries its own controller. Plug it into the rear socket and its screen appears on the terminal. Rate, section control and documentation come from that implement's ECU working with the terminal's Task Controller, if you have one.
Switched outputs you add yourself. A lot of what needs switching on a farm has no ECU at all: a work light, a diverter valve on the front loader, a hydraulic solenoid on an old trailer, a beacon. For those, add a relay module that speaks ISOBUS. ISOBUS Block is an 8-channel relay module that shows up on the terminal as its own screen, with buttons you name and assign to CH1 to CH8. Each button switches toggle (TOG) or momentary (MOM), one channel or several at once. How the screen, the buttons and the relay layer fit together is set out in the ISOBUS implement control guide.
ISOBUS Block uses the terminal's UT and AUX-N functions only. It is not a Task Controller client, so no documentation, no prescription maps and no GPS section control. A boom section switched from a button is switched by hand.
What to check before buying
- AUX-N support, if you want joystick control. AUX-N (Auxiliary Control, new type) lets you assign implement functions to physical buttons. Without it, you control the implement from the touchscreen only. Check the terminal lists AUX-N, and check it is active on your unit, not a licence you still have to buy. The AUX-N complete guide explains the assignment side.
- An AUX-N input device. AUX-N needs something with buttons. On many ISOBUS tractors the armrest joystick is already an AUX-N input device. On a retrofitted tractor it usually is not, because the tractor's own joystick is not on the ISOBUS network. Then you add an ISOBUS joystick that plugs into the in-cab socket: CCI, Müller-Elektronik and Reichhardt all sell one.
- Task Controller level, if you want section control or maps. TC-BAS logs totals. TC-GEO runs prescription maps and variable rate. TC-SC switches sections automatically from GPS position. Automatic section control needs TC-SC on the terminal, a GPS receiver and an implement whose ECU supports it. It is often an extra licence. The ISOBUS Task Controller guide explains the levels.
- Screen size for the cab. A 7" or 8" screen fits a compact tractor or sits beside the main display without blocking the view. A 12" screen shows two implements, or an implement plus guidance, at once. Measure the mounting spot and your sightline to the front before you choose.
- Software version. Functions and compatibility depend on the software version. Keep the terminal updated, and check the terminal maker's compatibility list and the implement maker's spec sheet against the version you actually run.
Frequently asked questions
What is an ISOBUS universal terminal?
A screen that can show and control any ISOBUS implement, whatever its brand. It can be the tractor's own display with the UT function, or a separate aftermarket terminal plugged into the in-cab ISOBUS socket. The implement sends its layout over the bus and the terminal draws it.
Can I retrofit an ISOBUS terminal to an older tractor?
Yes. If the tractor already has ISOBUS sockets, the terminal plugs into the in-cab socket. If it has no ISOBUS at all, you also need a retrofit kit with an in-cab socket, a rear 9-pin ISOBUS socket and a harness with power and bus termination. Most buyers have a dealer or an agricultural electrician install the kit.
Do I need a separate terminal for ISOBUS Block?
No. ISOBUS Block works on any ISOBUS UT screen: the tractor's own display or an aftermarket universal terminal. It shows up as its own screen with your named buttons, and you assign those buttons to the joystick through AUX-N.
What is the difference between VT and UT?
Nothing functional. Virtual Terminal (VT) is the name in the ISO 11783-6 standard. Universal Terminal (UT) is the industry name for the same function, used in conformance testing. Spec sheets and brochures use either. The Virtual Terminal explainer covers how it works.
Which ISOBUS terminal supports AUX-N?
Most current universal terminals list it. Whether it is standard or a licence you unlock depends on the model and software version, so check the terminal maker's compatibility list and the implement maker's spec sheet for your exact unit. Many ISOBUS tractors also support AUX-N on their built-in screen.
Need an ISOBUS relay module for controlling solenoids, work lights, or hydraulic valves? ISOBUS Block provides 8 relay outputs controlled directly from your tractor's Virtual Terminal display.