Cowasaki's electrical tutorial part 1
Part 2 of the tutorial has now been written with specific instructions for tests and checks.....
<CLICK HERE FOR PART 2>
Having seen numerous simple questions on car electrics/electrical systems I thought I would write a simple tutorial. I will create a few more on more specialised topics later if people find them useful. My way of thanking people for all the help they have given me over the past 6 months since I got my first landy.....
1 - The basics
Electrical systems are basically simple if broken down into small manageable parts. A basic electrical circuit consists of a power source (shown here as the battery), come connections (the wires shown here as green lines) and a load (shown here as a bulb). This is basically the simplest circuit.
As you can see from the above diagram the bulb is connected to the battery by two wires which creates the circuit. One side of the battery is shown as positive whilst the other is shown as negative. For our means, working on cars, there are several different ways of referring to these sides of the battery:
Positive = 12v, live, battery
Negative = 0v, ground, chassis, body
Bulbs are examples of devices that require being in the circuit but do not require being in the circuit in any particular direction so will also work if the positive and negative are swapped around as long as there is still a circuit. Other examples of components that can be wired either way with the same effect would be a heater element, relay or a buzzer.
Other components can be directional in that their operation reverses if the connections are reversed or that they only work one way or the other. Two components that you will often see in a car which have this characteristic are solenoids and motors.
If we add another bulb to the same circuit it can be connected in two ways:
This example shows what we call series, each bulb is connected one after the other.
This example shows what we call parallel, each bulb is connected independently to the battery.
In a car we like to use the parallel method when connecting bulbs as with the first method if the bulb failed then both bulbs would fail. Old Christmas tree lights used this method whereas the indicators on your Landrover use the parallel method so if one fails the other still works.
If you follow the two examples you can see that you can get from the battery to the bulb and back to the other side of the battery only by going through the other bulb in the series example but in the parallel example you have two paths. By removing one bulb completely you could still get around from the battery through the bulb and back to the battery.
When we have components in parallel we can treat each section as a separate series circuit. By breaking this circuit that component fails to operate and this is how things turn on and off in our cars.
The simplest way of breaking the circuit is to remove a wire so here is the circuit again twice with one of the wires disconnected in each example:
Both these circuits do the same in that they do nothing until the wire is reconnected. It does not matter that the disconnected wire is the negative or positive.
The first example has the negative wire disconnected and this is referred to a negatively switched, the second example has the positive wire disconnected and this is referred to as positively switched. Cars use this all the time and a good example are the dash warning lights in the Defender. Some such as the side light warning are positively switch i.e. the negative is permanently connected whilst the positive is only connected when the side lights are switched on. Other circuits such as the diff lock warning light have the positive permanently connected and the ground or negative is connected by the action of activating the diff lock.
If we introduce a new component, the switch, then this circuit becomes a circuit you will be familiar with:
This is effectively the circuit diagram of a torch! We have a battery, a switch and a bulb. The switch breaks the circuit and stops the bulb lighting. The switch can be anywhere in the circuit as unless the circuit is complete it will not light.
In cars we have a term negative earth or VERY rarely positive earth. This refers to the fact that on a car we often make one side of the circuit using the body shell. In the usual negative earth systems such as those used by Landrover we can treat the body of the car as if it were one giant negative wire.
In this example the battery is connected to the earth/ground/body and the positive goes via the switch to the bulb which is in turn connected to earth which makes the circuit. This explains why the lights often stop working on a Landrover because the earth connection gets broken. It also explains why often we have strange faults which appear to be unrelated but are in fact a faulty earth. From your knowledge now you should be able to check this, connect a jump lead from a good earth point to our suspected bad one. If the fault goes away you have found the fault.
Welcome To LandyZone!
LandyZone is the biggest Land Rover forum on the net. We have plenty of very knowledgable members so if you have any questions about your Land Rover or just want to connect with other Landy owners, you're in the right place.
Tutorial - car electrics.