A truck is a vehicle that is generally driven by a combustion engine.
Magnetic fields occur in three different frequency ranges:
1) in the low-frequency range under 20 Hz
2) in the power frequency range from 50 - 60 Hz
3) in the radiofrequency range.
In the power frequency range, the magnetic field is caused by the alternator and the cables from the alternator to the battery (especially when driving with full headlights), the starter motor and the according cables when switching on the motor, the ABS-system and electric window winders.