1972 VW Beetle Electrical System
The electrical system of 1972 VW Beetle is a 12V system. The battery supplies the power when the engine is below a certain speed. When the engine is running above this speed, the generator supplies the power and recharges the battery. Fuses in certain circuit protects the generator and battery from overloads caused by damage to the system. The electrical system as presented is broken down into the smaller circuits to make it easier to understand. The circuits are:
- Interior Lights
- Exterior Lights
- Automatic Stick Shift
Located on the fronten left side of the engine compartment is an electrical receptacle. This receptacle is used in manufacturing and diagnosis. It cannot be used without special diagnosis equipment. The cover on the receptacle should always be closed. Do not tamper with this receptacle.
When the engine is not running, the battery supplies the power to the system. As engine speed increases, the generator starts to produce voltage. When the voltage is large enough, it causes a relay in the regulator to connect generator output to the system and the battery. If the generator output decreases past a set voltage, the regulator will disconnect the generator from the system and prevent the battery from discharging through the generator. A generator warning light is installed in the instrument panel. This light indicates when the battery is supplying power to the system. Power to one side of the light is supplied by the battery through the ignition switch. When the engine is running below generator cutout speed, the light is lit. When generator output is large enough, it applies power to other side of the light and the light will go out.
Electrical power is supplied from the battery to a terminal of the starter solenoid and to a terminal on the ignition switch. When the ignition switch is turned, power is applied to the coil of the solenoid. This power causes the solenoid to move the gear on the starter into contact with the flywheel. As the solenoid moves it closes a switch which applies power to run the starter. After the engine starts and the ignition switch is release, power is removed from the solenoid and it returns to normal. A spring in the starter gear moves the gear back out of contact with the flywheel.
With the ignition switch on, battery or generator output is supplied through the switch to the primary of the coil, automatic choke, and pilot jet. Voltage is applied direct to the choke and pilot jet to regulate fuel flow. The ground circuit of the coil is through the distributor points. As the distribuotr shaft rotataes, it opens and closes the point to make and break the circuit to ground. When the points are closed, power flows through the primary winding of the coil producing a force in the secondary of the coil. When the points open, the force in the secondary collaposes, creating an high voltage output. This output is applied to the rotor of the distributor as the rotor comes in line with a contact in the distributor cap. The contact passes the power to a spark plug. This high voltage causes the current to arc across the gap between the spark plug elements and ignites the fuel mixture in the cylinder. This takes place four times in one rotation of the distributor shaft with the power being directed to each plug in proper sequence.
The wiring diagram of 1972 VW Beetle can be found here.