Many electrical accessories in the vehicle utilize relays to transmit current to the component, and if a relay is defective, the component won't operate properly. Most relays are located in the engine compartment fuse and relay box, while some can be found in other parts of the vehicle or in various wiring harnesses underneath the instrument panel. If a faulty relay is suspected, it can be removed and tested, either by following a specific procedure or by a dealer service department or repair shop, with defective relays needing to be replaced as a unit. Most relays used in these vehicles are often referred to as "ISO" relays, which are standardized by the International Standards Organization, and their terminals are numbered to indicate usual circuit connections and functions, with two basic layouts present. To determine proper connections for testing, a wiring diagram for the circuit should be consulted, and if that is not possible, the following information may assist. Two terminals are for the relay control circuit, connecting to the relay coil, while the other terminals are for the power circuit; when energized, the coil creates a magnetic field that closes larger contacts to provide power to circuit loads. Terminals 85 and 86 typically serve as the control circuit, with specific connections required if a diode or resistor is present. Terminal 30 is usually connected to the battery voltage source for circuit loads, while terminal 87 connects to the ground side of the circuit. An ohmmeter can be used to check continuity through the relay control coil by connecting the meter according to polarity, reversing the leads for a second check, and interpreting resistance values based on the presence of a resistor or diode. Continuity should be checked between the relay power circuit terminals, ensuring no continuity between terminal 30 and 87 when the relay is not energized. By connecting a fused jumper wire to terminal 86 and the positive battery terminal, along with another jumper wire between terminal 85 and ground, the relay should click, and continuity should then be present between terminals 30 and 87. If the relay fails any of these tests, it should be replaced.
