Which measurements can I take myself when troubleshooting?
Four measurements with a multimeter are enough: battery voltage (typically 13.8–14.4 V with the engine running), terminal voltage while cranking (must not fall below 10.5 V), the voltage at the unit's supply terminals and the continuity resistance of the chassis connection. On the LFT20 a bench test is also performed by touching the wires directly to the battery.
The measurements to take, in order:
- Battery, ignition off: A rested battery should be above 12 V.
- Alternator charging: Typically 13.8–14.4 V with the engine running. It is normal for it to read 14.0–14.2 V just after start-up and to settle around 13.8 V once the battery is full.
- While cranking: A sound battery must not drop below 10.5 V at the terminal during cranking; above 11 V is good. 8–9 V and below points to a problem with the battery, wiring, chassis or starter motor.
- Unit terminals: There must be voltage at the unit's supply terminals while the command is given. If there is a noticeable drop under load, the cross section or the contact is inadequate.
- Chassis continuity: The resistance between the negative terminal and clean chassis should be almost zero.
- Bench test: Red wire to battery positive, black wire to battery negative; if the motor turns in both directions the unit is sound.
While measuring, never disconnect the battery terminal with the engine running. If you note the results down and include them in your support request, diagnosis becomes much faster.
Full topic: Converting a tractor hydraulic lever to electronic control