In the vehicle, other electrical accessories include, the fuel injection system; the starter motor, the fog lamps; all of which use relays to switch electrical signals to them. Relays work on a low current control circuit for a high current power circuit and any bad relay will not enable the right action of the related component. Majority of the relays are in the engine compartment fuse/relay boxes and there are some limited relays above the interior fuse box in the dashboard. If a faulty relay is purported, then it has to be removed and tested, either following a certain process or taken to a dealer service department or a repair shop and since relays are sold and distributed as complete assemblies, deteriorated relays have to be replaced in their entirety. The four types of relays used are; there are types which are normally closed and there is current passing through one circuit till is gets tripped and breaks that circuit and closes another one. Conventionally, two of the terminals are used for the relay control circuit that connects towards the relay's coil while the other terminals connect to the power circuit that is internally connected when the control circuit is energized. Controlling and power circuit terminals of some relays may be marked and if not, wiring diagrams can help in determining the right wiring. When testing a relay, an ohmmeter should be connected between the power circuit terminals expecting the circuit to have no continuity. For a rather conventional 'four-terminal', normally open relay, it should have continuity when energized and should not have continuity when de-energized. One of the terminals of the control circuit should be fused to the positive terminal of the battery and the other terminal of the control circuit should be fused to ground; on closing the relay there should be a clicking sound and there should be continuity when measured on the meter. If the relay does not click, it will be require the jumper wires be switched. If the relay does not work as expected each time it is given as a test, it should be replaced.