The device consists of only three parts: the thyristor VS1, diode VD1 and the reed switch SF1 (Fig.1).The thyristor VS1 performs the role of an electromagnetic relay, which is triggered by the presence of even a short pulse on the control electrode. This signal is fed with the closure of the reed switch SF1 installed in the cabin. The thyristor open, its resistance decreases sharply, and the battery terminal "-" is connected to "weight".
The thyristor current flows only in one direction - from the battery to the vehicle's electrical system. So that the battery could be recharged from the generator, in parallel with the thyristor in reverse polarity included diode VD1.
When the ignition is off or muted the motor, the device goes into "anti-theft" mode. Place the device under the hood in a remote place, so it is not evident to an outsider or intruder. In the case of the thyristor is desirable to make the hole for M8 screws for terminals (Fig.2). Reed switch SF1 is mounted in the cabin quietly - on plastic decorative panel or in any other place. Magnet reed switch is kept by the driver.
The described device has been installed in the car "FORD ESCORT" and effectively operated for over two years.
Author: V. Raskov, Vitebsk; Publication: N. Bolshakov, rf.atnn.ru