Various electrical gadgets in the vehicle for instance relevant injection system,
Horns, starter and the fog lamps employ relays to send an electrical signal to the component. Relay controls the low current control circuit to govern the high current power circuit, and when the relay is faulty the particular device cannot function as required. Bulk of relays can be found at the fuse and relay box and if a relay is deemed abnormal it can be taken out for testing or better yet to the dealer service department as all bad relays should be replaced. The relays mainly in use are the ISO relays in which the provision for the circuit connections has been numbered and each having its specific function. Two of the pins are used for the control circuit that connects to the relay coil, the rest are pins in the power circuit. When energised the coil produces a magnetic field to close the larger contacts of the power circuitry to supply power to the loads. Normally terminals 85 and 86 are for the control circuit definite connection is necessary if Diode or Resistor is provided is provided. Terminal 30 allows the battery voltage to be connected , while terminal 87 connects to the ground of the circuit in question. In the testing of the relay, the sensitivity can be checked by measuring the resistance through the control coil and comparing it with the correct resistance in both directions. In the same way, it is permissible for the continuity between terminal 30 and 87 to be disrupted when the relay is without energy. Jumper wires should be connected to the proper terminal and the battery to check if the relay made a clicking sound; continuity test should also be performed and the power circuit terminals are should also be tested. If any of these tests show failure the relay should be changed.