Flow of Diagnosis
Before commencing
Check that the battery is clean since dirt may cause short-circuiting between the terminals. If necessary, wash the battery with lukewarm water and wipe clean, taking care to ensure that dirt does not enter any of the cells.
Check the electrolyte level, state of charge and general condition of the battery
If the charge is low, recharge the battery or install a fully-charged and otherwise perfect replacement. Battery charging must not be carried out during fault tracing and testing since values measured under these conditions will be incorrect.
Check the system for faulty or defective leads and insulation, loose or corroded cable terminals, ground connections and fuses
Inspect the alternator belt to ensure that it is not cracked or otherwise damaged. Ensure that the belt is correctly tensioned. In addition, the belt must not be allowed to bottom in the pulley, but must ride only on the flanks of the groove. Bottoming indicates that the belt is over-tensioned, worn or the wrong type, or that the pulley itself is worn.
If twin belts are fitted, both must be replaced
The belts must be of the same quality to ensure that the load is distributed equally between them.
Caution! Watches, rings, armbands and such like articles may cause short-circuits when working on electrical systems, resulting in personal injury.
Fault tracing
Electrical system faults may be divided into the following three main categories:
Loss of supply
Faulty ground connections
Short-circuits
Loss of supply
Loss of supply means that one or more circuits is out of service. Use a test lamp or voltmeter to localize the fault. Commence by checking for voltage at the appropriate fuse. If voltage is present at each side of the fuse, continue by checking for supply at the circuit connectors in order to localize the point of breakage. If voltage is present at all points of the circuit and the circuit components are intact, the ground connection is faulty.
Faulty ground connection
If the fault is not due to loss of supply or to a faulty component, the circuit ground connection may be faulty or open-circuited. This may be checked by connecting a temporary ground lead between the component in question and the body. If this eliminates the fault, repair the normal ground connection.
Spurious indications by one or more of the panel instruments, or faint illumination or flashing of the warning lamps (often in step with the flasher relay) may also indicate a faulty ground connection. (In this case, a component may be attempting to establish a ground connection across another component.)
Short-circuits
If a fuse fails when the circuit in question is used, commence by checking that the fuse rating is correct. If the correctly rated fuse continues to fail, check the ratings of the other fuses. Since some fuses may be connected in series the main fuse and an individual circuit fuse), the last fuse in the circuit should be of a lower rating than the first to protect only part of the circuit only.
However, if the last fuse has been replaced by one of a higher rating than the first, the latter may fail, resulting in confusion when carrying out fault tracing. The specified rating of a fuse must never be increased. Persistent failure of the fuse despite correct rating of all the fuses indicates the presence of a short in the circuit (assuming that overloading is not being caused by the connection of an additional consumer).
If a short-circuit is present, isolate the circuit in question (for example, by removing the fuse), and use an ohmmeter to check the circuit and locate the fault.
If an ohmmeter is not available, test the circuit as follows:
- Disconnect the power supply to the circuit before the fuse.
- Open the first connector after the fuse.
- Reconnect the power supply.
- If the fuse remains intact, the circuit as far as the connector is fault-free.
- Again disconnect the power supply before the fuse.
- Reconnect the circuit at the first connector and open the second connector after the fuse.
- Reconnect the supply.
- If the fuse remains intact, the circuit as far as the second connector is fault-free.
- Repeat the procedure for each subsequent connector.
Failure of the fuse indicates that the short-circuit is located between the last connector to be opened and the immediately preceding connector (at which the fuse remained intact).
The following precautions should be observed to avoid damage to the power supply system (alternator and regulator) during fault tracing:
- Use permanent connections, avoiding temporary connectors such as crocodile clips, for ammeters etc. In addition to the likelihood of voltage drops leading to incorrect readings, devices of this type are prone to loosening.
Disconnection of a lead under these conditions may cause irrepairable damage to the alternator and regulator.
- The alternator and regulator must be tested in combination with the battery.
- Connection or reconnection of the instrumentation, as well as other work on the power supply system, may be carried out only when the alternator has stopped and the ignition has been switched off or the battery ground lead disconnected.
- Overvoltage faults must, without exception, be rectified since the life of the component(s) affected will otherwise be severely reduced.
- Avoid replacing components without having established the fault.
Use the appropriate wiring diagram and fault-tracing chart for fault-tracing purposes.
Color coding of leads in wiring diagram
The leads shown in the wiring diagram are color codes, with the codes denoted by letters. Each code (with the exception of black) consists of one or two letters representing an abbreviation of the color in English.
SB Black
R Red
Y Yellow
GN Green
BL Blue
GR Grey
W White
BN Brown
OR Orange
V Violet
P Pink
Multicolored leads are identified by the individual color codes separated by an oblique stroke. Example: A blue and yellow lead is denoted BL/Y.
Connectors
Wiring leads are normally joined by connectors, the pins of which are numbered as shown in the adjoining illustration.