[jakobnev]

The kit is just connected to the battery, it senses that the engine is on from high frequency components in the battery voltage(i assume). The brushed DC-motor generates an HF voltage ripple and the diodes keep the voltage across the motor down. (without them the motor spins really fast and the light dim)

The kit also has a wire that connects to your normal light that dim the LEDs when your other lights are on.

I turn the engine off with the ignition switch.