GENERAL INFORMATION

The electrical system operates at 12 volts and uses a negative ground. Power for the headlights and all other electrical components is supplied by a lead-acid battery, which is recharged by the alternator.
This chapter describes repair and maintenance procedures for various electrical components not related to the engine.
Note that when working on the electrical system, disconnect the negative battery cable to prevent short circuits and/or fire.

* If your vehicle's stereo has an anti-theft code system, make sure you know the radio activation code before disconnecting the battery.

Electrical System Troubleshooting

A typical electrical circuit consists of an electrical component, switches, relays, motors, fuses, fusible links or circuit breakers, and wires and connectors that link all components together and connect them to the battery and vehicle ground. To simplify troubleshooting, wiring diagrams for the vehicle electrical system are provided at the end of this chapter. Before beginning to check a faulty circuit, first study the schematic of that circuit to understand its components. The source of the fault can be found faster if you determine which components of the circuit are operating normally. If several components or circuits fail at once, the problem is likely a blown fuse or poor ground, since one fuse often protects several circuits.
Electrical system problems are usually caused by simple reasons such as corroded or loose connections, a blown fuse, a blown fusible link or a faulty relay. Visually inspect the condition of all fuses, wires (where possible) and connectors in the faulty circuit before checking other components of that circuit. If you are going to use test instruments, use the circuit schematics to determine which connections must be checked to locate the fault.
The main tools required for troubleshooting an electrical circuit are a voltmeter (or a 12-volt test lamp with connecting leads), a continuity tester, a battery with jumper leads, and a fused jumper wire, preferably with a circuit breaker, that can be connected in parallel to the circuit. Before starting fault diagnosis with test equipment, study the wiring diagrams to determine the connection points.

VOLTAGE CHECK
Perform a voltage check if an electrical circuit is malfunctioning. Connect one probe of the test light to the negative battery terminal or to vehicle ground. Connect the other probe to a connection point in the circuit being tested, preferably located as close as possible to the battery or fuse. If the test light illuminates, voltage is present, which means the part of the circuit between the connection point and the battery is good. Continue testing the remainder of the circuit in the same way. When you find the point where voltage is absent, the malfunction is between this point and the last point where voltage was present. Most problems are caused by poor connections.

* Remember that in some circuits voltage is present only when the ignition key is turned to a specific position.

SHORT CIRCUIT DETECTION
One method of locating a short circuit is to remove the fuse and connect a test light or voltmeter to the fuse terminals while all other electrical components in this circuit are switched off. There should be no voltage in the circuit. Move the wires from side to side and watch the test light. If it illuminates, a wire is shorting somewhere in this area, probably where the insulation has worn through. The same test can be performed on any other circuit component, including the switch.

GROUND CONTINUITY CHECK
Perform a ground continuity check to verify that an electrical component is securely connected to vehicle ground. Disconnect the battery and connect one lead of the continuity tester to vehicle ground. Connect the other lead to the connection or ground point to be checked. If the test light illuminates, the ground is good.

CIRCUIT CONTINUITY CHECK
Continuity check is required to determine whether there is an open in the circuit. Disconnect power from the circuit and check the circuit for continuity using a test light with a power source connected. Connect the test light leads to the ends of the circuit (or to the positive end and vehicle ground); if the test light illuminates, there is no open in the circuit. If the light does not illuminate, there is an open somewhere in the circuit. Similarly, a switch can be checked by connecting the test light to the switch terminals. After the switch is turned on, the test light should illuminate.

LOCATING AN OPEN CIRCUIT
Locating an open circuit visually can be quite difficult, since corroded or poor contact connections are often hard to see. Sometimes simply moving a connection wire or a wire in the harness will eliminate the malfunction. Unreliable operation of electrical components is also often caused by corroded or poor connections.
Locating a malfunction in the electrical system is fairly simple if you understand that the electrical system operates on the principle that current flows from the battery through wires, switches, relays, fuses and fusible links to electrical components (lamp, motor, etc.) and to vehicle ground, from where it returns to the battery. Any malfunction in the electrical system represents an obstruction to the flow of current from or to the battery.