Electrical Systems

The electrical system on a vehicle includes the battery, alternator, starter motor and ignition switch, instruments and gauges, lights and wipers, and also wiring and fuses. At St. Amand Auto & Truck Repair in St. Catharines we have qualified technicians who are able to handle all of your electrical system needs and use the latest technology to help diagnose any problem you may have.


The battery stores electricity and supplies current to the vehicles electrical system when needed. The alternator would normally fulfill this need when the engine is running but there are occasions when the power is needed and the engine is not running. An example of this would be when the starter motor is operated or the parking lights or radio used when parked with the engine off. Most cars have a 12 volt battery, which is really six separate two volt cells joined together. If current is continually drawn from the battery without recharging then it will go flat and will need to be charged from an outside source (battery charger).


Modern vehicles use an alternator in the charging system. The alternator is light and smaller and charges at lower engine speeds. A fan belt drives the alternator, but will not generate electricity until the engine is running. A magnetic field called a rotor is at the centre of the alternator. There are conductors fitted to the side of the alternator called the stator. When the engine runs the rotor spins and produces electricity. This electricity is then sent to recharge the battery and feed current to the electrical system.

Starter Motor and Ignition Switch

Starter motor
The starter motor is a small electric motor fitted with a gear called a pinion. The pinion engages with teeth on the flywheel and turns the crankshaft. When the ignition key is turned to the start position, the starter motor solenoid is engaged and current is drawn from the battery. This causes the starter motor to turn and engages the pinion with the ring gear. When the engine starts turning faster than the starter motor, the pinion disengages.

Ignition switch
The ignition switch directs the current to the ignition system, the starter motor solenoid and the fuse box to feed the various accessories.

Instruments and Gauges

All vehicles have a selection of instruments and gauges. Every vehicle has a speedometer, which can be operated by a cable from the transmission or wheels, or can be electrically operated by a transducer from the transmission which generates current, the faster it spins the more current it generates and the speedometer converts this current into movement of the speedometer needle and odometer.

A variable resistor in the fuel tank, which is attached to a float, operates the fuel gauge. Current is fed through the gauge to the resistor. The amount of resistance varies with the level of fuel in the tank and this determines where the needle on the gauge will sit. Remember that the fuel gauge is just an indication of the fuel level not an accurate analysis of much fuel is present.

The temperature gauge is mounted in the instrument cluster and is operated by a sending unit mounted in a water jacket in the cylinder head. It works much the same as the fuel gauge, except that the resistance is varied by engine temperature rather than movement of a float. When the engine is cold the resistance in the sending unit is high and a small amount of current flows through the gauge. As the engine heats up the resistance becomes less and the needle in the gauge rises. The instrument cluster also contains warning lights for various electrical systems. Most lights work on the principle that when the circuit is inoperative the light is on.

Lights and Wipers

The electrical current that operates the lights is drawn from the alternator when the engine is running, and the battery when the engine is running too slow for the alternator to produce enough current, or the engine is stopped. Most of the light bulbs have a single filament which heats up and glows when current is applied. However there are some exceptions, most headlamp bulbs have two filaments, which heat at different rates. The main beam glows brighter than the dipped beam. The brake light and rear parking light are often incorporated into the same bulb. This bulb also has two filaments. The indicators are operated through a flasher unit, which quickly switches on and off the current to the bulb. A switch that is attached to the brake pedal operates the brake light. When the pedal is depressed the switch comes on and operates the lights, when the pedal is released the switch turns off.

The wipers are operated by a small electric motor. When the wipers are switched on, current is sent to the motor and this moves a set of linkages, which are attached to the wiper arms. Different wiper speeds are achieved by varying the voltage to the wiper motor.

Wiring and Fuses

Wiring distributes the current from the battery to all the electrical components. It also carries signals from sensors and switches. The wires in your car are not the same thickness. This is because some wires carry a large amount of current, like the connection between the battery and the starter motor and some carry very little current like the wires to the fuel injectors. A large current going through a small wire will cause it to overheat and melt.

Fuses protect the wiring. They form a bridge in the electrical circuit. If the circuit overloads for any reason the fuse will blow and break the circuit. Most vehicles have more than one fuse panel. Your owner’s handbook will indicate the position of the fuses and the size of fuse used for each circuit. The fuse contains a small wire inside, which is designed to melt before the wiring in the circuit melts. A visual check of the fuse will tell you if it is blown. You must always replace blown fuses with the correct amperage replacement.


Heavy Duty Emissions Facility
When it comes to auto repair, you need someone you can trust. With years of experience providing auto repair to vehicles all across St. Catharines and the Niagara Region, St. Amand Auto & Truck Repair has the vehicle maintenance services you need.


Monday - Friday: 8:00 AM - 5:00 PM
Saturday: CLOSED

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132 Bunting Rd, St. Catharines, ON L2P 3G5