Which ignition detection method fits which vehicle?
A tracker knows the ignition state in one of three ways. It reads a switched wire, it reads the supply voltage, or it senses motion. Each one answers a slightly different question, and each one fails on some vehicles.
- Suits it
- Usable with a cross-check
- Weak
| Vehicle type | Ignition wire (ACC or IGN) | Supply voltage | Motion (accelerometer or GNSS speed) |
|---|---|---|---|
| Petrol or diesel car or van, 12 V | Suits it | Suits it | Usable with a cross-check |
| Truck or bus, 24 V | Suits it | Suits it | Usable with a cross-check |
| Start-stop or smart-alternator vehicle, 12 V | Suits it | Weak | Usable with a cross-check |
| Mild hybrid | Suits it | Weak | Usable with a cross-check |
| Full hybrid or electric vehicle | Usable with a cross-check | Weak | Suits it |
| Generator, equipment or PTO-driven machine | Suits it | Suits it | Weak |
Built-in fit rules for the key and engine choices in the finder. They are not a measurement of your vehicle.
- The wire follows the key. It is the cleanest choice on a conventional vehicle and the only one that does not depend on the charging system.
- Voltage follows the alternator. It shows the engine running, but a smart alternator, start-stop or a hybrid converter can fool a fixed threshold.
- Motion shows that the vehicle is in use. It misses machines and PTO work that run while standing still.
How do you connect the ignition wire?
Find a wire that is live only with the key on. Test it with a multimeter with the key off, in accessory and on. Then run it to the ignition input of the device, next to the constant supply and ground.
A wire that carries a heavy load, or that stays live in accessory mode, gives wrong states or damages the vehicle circuit. Disconnect the battery before you cut or splice, and follow the vehicle wiring information.
How do you set a voltage threshold?
Measure at the battery, or at the device supply, in two states. Park the vehicle with the engine off and note the highest reading. Run the engine, idle and drive, and note the lowest reading. The threshold goes in the middle of the gap.
gap = lowest running reading - highest parked reading, at least 0.6 V (typical)Result = 13.2 V from 12.6 V and 13.8 VThe typical engine-on band is only a guide. Your readings decide.
Add a delay before the device accepts a change, so a short dip while cranking or a heavy load does not flip the state. Add hysteresis, a low and a high threshold, so a reading that sits on the line does not flicker.
What does the parked voltage say about the battery?
A rested lead-acid battery has a voltage that follows its charge. The table is for 12 V. Read a 24 V pair as two 12 V batteries.
| Open-circuit voltage | Approximate charge |
|---|---|
| 12.65 V or more | about 100 percent |
| 12.45 V | about 75 percent |
| 12.24 V | about 50 percent |
| 12.06 V | about 25 percent |
| 11.89 V or less | empty |
Rested means 4 hours or more with no load and no charge. Battery makers recommend 24 hours, and the table was read after a 24-hour rest at 26 °C. Right after the engine stops, the reading is too high. Treat the rows as bands, not exact points. Source: the BCI table as given in the public battery article BU-903, checked 2026-11-03.
What does the vehicle electrical environment look like?
A vehicle supply is not a steady 12 or 24 V. It dips when the starter turns, runs above nominal when the alternator charges, and can spike when a load is switched off. The Power range tab checks your device range against these values.
| Parameter | 12 V system | 24 V system |
|---|---|---|
| Nominal running supply | 13.5 VISO 7637-2 | 27 VISO 7637-2 |
| Highest continuous supply | 16 VISO 16750-2 | 32 VISO 16750-2 |
| Load-dump test pulse, peak | 101 Vverify | 202 Vverify |
| Cranking dip, lowest seen | 6 Vtypical | Not found: measure it |
| Engine-on band on the supply | 13.2 to 16 Vtypical | 27 to 32 Vtypical |
Checked on 2026-11-03 in the official previews: 13.5 V and 27 V are the test supply voltage UA of ISO 7637-2 (13.5 ± 0.5 V and 27 ± 1 V). 16 V and 32 V are the highest supply voltage of ISO 16750-2:2023, Tables 3 and 4. The load-dump peaks 101 V and 202 V are still from public notes, because that clause is not in the preview. The 24 V cranking value was not found. Take real values from the standard or from your vehicle maker.
Worked example: a diesel van, 12 V
The defaults in the finder describe this van. The installer reads the battery with the van parked and again with the engine running.
- Method: the key position is wanted and a switched wire is available, so the ignition wire is the first choice. Voltage is the cross-check.
- Readings: parked 12.4 to 12.6 V. Idling 13.8 to 14.0 V. Driving 13.9 to 14.3 V.
- Gap: 13.8 - 12.6 = 1.2 V, above the 0.6 V minimum.
- Threshold: (12.6 + 13.8) / 2 = 13.2 V. Low 13.1 V and high 13.3 V with 0.2 V hysteresis.
- Battery: the lowest parked reading 12.4 V is about 50 to 75 percent when the battery has rested.
- Power range: with a typical 9 to 36 V device, the supply checks pass. The cranking dip, load dump and reverse polarity need a check against the datasheet.
What mistakes do installers make?
- Using the accessory wire when the report needs engine running.
- Measuring the parked voltage minutes after the engine stops, when the surface charge is still high.
- Setting one threshold for every vehicle in a mixed fleet. Measure each type.
- Trusting voltage on a hybrid, an electric vehicle or a start-stop vehicle without a second method.
- Leaving no delay, so a short voltage dip while cranking flips the state.
- Forgetting that a battery charger or solar panel can raise the voltage with the engine off.
Assumptions and limits
Fit scores are rules of thumb for a vehicle type. They are not measurements of your vehicle, and a particular model can differ. The engine-on bands, delays and device supply range are typical values you can edit. The nominal and highest vehicle voltages were checked against ISO 7637-2 and ISO 16750-2. The load-dump values are public notes: verify them. The finder does not read your device, does not know which methods a Tracom model supports and does not say that any vehicle or device meets a standard. Always test on the real vehicle.