18.2. Electric chains

The usual electric chain consists of elements of the electric equipment, switches, the relay, engines, safety locks, fusible inserts and wires and sockets which connect all elements among themselves, the rechargeable battery and "mass" of the car.

The cause of defect can be found much quicker if to define what of elements of this chain work normally. If several elements or chains fail at once, the problem probably consists in the fused safety lock or bad grounding as often one safety lock protects several chains.

Problems with work of system of electric equipment are usually caused by the simple reasons, such as the oxidized or unreliable contacts, the fused safety lock, the fused fusible insert or the faulty relay. Visually check a condition of all safety locks, wires and sockets in a faulty chain before check of other elements of this chain.

The main devices necessary for failure detection in a chain are:

   – a tester or the voltmeter (or a bulb on 12 V with connecting wires);
   – a control bulb with the power supply (or the device for check of integrity of chains);
   – an ohmmeter (for measurement of resistance);
   – rechargeable battery;
   – probes with wires;
   – a cap wire, it is desirable with the automatic switch or a safety lock which can be used for check of wires or elements of the electric equipment.

For detection of unreliable connection or the place of short circuit (usually because of the bad or polluted connection, or the damaged isolation) wires can be shaken by a hand to see whether the chain fails at the movement of a wire. In such way it is possible to find a point with the unreliable socket or a point in which there is a short circuit.

Besides the problems connected with unreliable connection, the electric chain can have two other main malfunctions – existence of break in a chain or short circuit.

The break in a chain can be caused by a rupture of any wire or lack of connection in a chain that will prevent a current of current. The break in a chain will cause refusal of any element of the electric equipment in work, but will not lead to burn-out of a safety lock protecting this chain.

The malfunctions connected with short circuit are caused by short circuit in a chain that leads to the fact that the current flowing on a chain begins to flow on other chain, and most often, leaves on "weight". Short circuit is usually caused by a rupture of isolation that allows the feeding wire to concern either other wire, or the grounded element, such as a body. Short circuit leads to burn-out of the safety lock protecting the corresponding chain.

Before search of a source of malfunction or when carrying out repair in system of the electric equipment, keep in mind that various types of wires have various color.

For detection of a rupture of a chain connect one of probes of a control bulb to the negative plug of the accumulator or "mass" of the car.

Connect the second probe to connection in the checked chain, it is desirable located as it is possible closer to the rechargeable battery or a safety lock.

Give tension on a chain. Do not forget that in some chains tension moves only at turn of a key in the ignition lock in a certain situation.

If tension is present (what the lit-up control bulb or indications of the voltmeter will testify to), it means that a part of a chain between connection and the rechargeable battery is serviceable.

Continue check of other part of a chain in the same way.

When the point where tension is absent is found, it means that the source of malfunction lies between this point and the previous point where tension was present. The majority of problems is caused by bad connection.

The negative plug of the rechargeable battery is connected to "mass" of the car – to metal of the engine / transmission and a body of the car – and the majority of systems of the electric equipment are developed so that one feeding wire approached an element of the equipment only, and current came back through car body metal. It means that fastening of an element of electric equipment and a body of the car are a part of an electric chain. Therefore, the bad or oxidized fastening can be the reason of a large number of malfunctions in system of the electric equipment, from a full exit of a chain out of operation before its unreliable work. In particular, bulbs can dimly burn (especially if other chain using the same point of grounding is included), engines (for example, engines of screen wipers or the fan of a radiator) can slowly work and inclusion of any chain can influence work of other chain. Notice that on many cars the connecting grounding strips between various units of the car, for example, between the engine / transmission and a body are used, i.e. usually when between elements there is no metal contact because of use of rubber fastenings, etc.

For check of reliability of grounding disconnect the rechargeable battery and connect one of ohmmeter probes to "mass" of the car. Connect the second probe to a wire or a point of grounding which needs to be checked. Resistance registered by an ohmmeter has to equal to zero: otherwise, check connection as follows.

If you consider that connection not as it should be, investigate connection and smooth out a contact surface and the plug of a wire or a surface of the grounded element to pure metal. Remove completely dirt and traces of corrosion, then, by means of a knife remove a paint coat to receive reliable compound of metal with metal. At assembly, reliably record connection; at installation of the plug of a wire, use gear washers between the plug and a body. After connection, for prevention of formation of corrosion apply a layer of vaseline or silicone lubricant on connection.