General information about troubleshooting electrical circuits (BMW 5 Series E28)

A typical electrical circuit consists of an electrical component, switches, relays, motors, fuses, fuse links, or circuit breakers connected to that component, and the wiring and connectors that link the component to the battery and chassis. To help you troubleshoot an electrical circuit, there are Basic electrical circuit diagrams.

Before attempting to repair any faulty electrical circuit, first study the wiring diagram to fully understand what it consists of. For example, you can sometimes narrow down the scope of a fault by checking the operation of other components associated with the circuit. If several components or circuits have failed at once, the problem may be in the fuses or grounding, as many circuits often share a single fuse and ground connection.

Electrical circuit faults usually result from simple causes such as loose or corroded contacts, a blown fuse, a melted fuse link or a faulty relay. Therefore, before you start looking for damage, visually inspect the condition of all fuses, wires and contacts in the faulty circuit.

The basic tools needed to troubleshoot an electrical circuit include a tester, a high-impedance digital voltmeter, a continuity tester, and jumper cables with a built-in circuit breaker that is used to bypass the circuit components. Before attempting to troubleshoot with test tools, consult the wiring diagram to determine where to connect them.

Checking the voltage in the circuit

A voltage test is performed when a circuit is not functioning properly. Connect one end of a circuit tester to the negative battery terminal or to a good ground.



Connect the other end to one of the terminals of the circuit being tested, preferably the one closest to the battery or fuse. If the tester light comes on, there is voltage in the circuit, which in turn means that the section of the circuit between the terminal and the battery is OK. Continue testing the remaining sections of the circuit in the same way.

When you reach the area where there is no voltage, you will find the fault location. Most often, the problem is a bad connection.

Remember that some circuits only have voltage when the ignition is on.

Finding a fault in a circuit is a fairly simple matter if you remember that any electrical circuit is electricity flowing from the battery through wires, switches, relays, fuses and fuse links to various components of the electrical circuit (light bulbs, motors, etc.) and to the ground, from which it passes back to the battery. And any fault in the circuit is a disruption in the flow of electricity from or to the battery.

Finding the location of a short circuit

One method of finding a short circuit in a circuit is to disconnect the fuse and connect a test light or voltmeter in its place. There should be no voltage in the circuit. Move the wiring from side to side, watching the test light. If the light comes on, then there is a short to ground in that area, probably because the insulation has worn through somewhere. Each component in the circuit is checked in the same way, right down to the switch.

Grounding check

Perform a ground test to check if a circuit component is properly grounded. Disconnect the battery and connect one end of a continuity tester to a good earth ground. Connect the other end to the wire or connector of the ground you are testing. If the light comes on, the ground is correct. If it does not come on, the ground is incorrect. In this case, disconnect the connector and thoroughly clean all connecting parts. When reconnecting the connector, use serrated washers if possible and tighten all bolts and other fasteners securely.

If your car radio is equipped with an anti-theft system, make sure you have entered the correct code before disconnecting the battery cable. Refer to Section Anti-theft audio system and instrument cluster language before disconnecting the wire.

If after connecting the wire, the inscriptions on your instrument panel appear in a language other than the one you need, refer to Section Anti-theft audio system and instrument cluster language, which describes the procedure for installing the required language.

Checking the conductivity of the circuit

A continuity test is used to determine if the circuit has any breaks - whether it conducts current well. A continuity tester is used to check, and the current in the circuit is turned off. Attach the connecting wires to both ends of the circuit, and if the test light comes on, then the circuit conducts current well. If the light does not come on, then there is a break somewhere in the circuit. The same procedure is used to check a switch, only the continuity tester is connected to the switch terminals. When the switch is on, the light should come on.

Finding an open circuit

Visually locating a possible open circuit is often difficult because oxidation or displacement of contacts is hidden by connectors. Open circuits are often caused by oxidation or loose contacts. Simply wiggling a connector contact on the sensing element or in the wiring can restore an open circuit, at least temporarily. Disconnect the connector and spray it with water from an aerosol can. On simple connectors, you can sometimes gently bend the connector contacts inward to improve contact - but do not get carried away with this, or you may damage the connector.