Fuses, Switches, Circuit Breakers And Relays
Check under hood and under the dash driver's side.
There may be a sticker on the inside of the panel cover that tells you the legend. Otherwise, it requires testing each and every one of those fuses, preferably with a fuse tester that can do it more expediently than pulling each one out and looking for a broken conductor.
Most vehicles use one or more fuse panels. This one is located on the driver’s side kick panel
It is possible for large surges of current to pass through the electrical system of your vehicle. If this surge of current were to reach the load in the circuit, this surge could burn it out or cause severe damage to the vehicle’s electrical system. It can overload the wiring, causing the harness to get hot and melt the insulation. To protect vehicle wiring, fuses, circuit breakers and/or fusible links are typically installed into the power supply wires throughout the electrical system. These items are nothing more than a built-in weak spot in the system. When an excessive amount of current flows through a circuit it causes an increase in heat throughout the wiring. Fuses and circuit breakers are designed as the weak link in the system and will disconnect the circuit to prevent damage to the components contained within that circuit. Components are equipped with connectors so they may be replaced in situations where they were damaged due to a power surge.
The following are descriptions as to how fuses and circuit breakers protect the electrical system:
- Fuse- A fuse is a weak link in the system designed to create an open circuit when the amperage flowing through that circuit exceeds the limits of the fuse. As the amperage increases, the conductor within the fuse heats up and eventually melts and breaks apart. This open circuit interrupts the flow of current and protects the components in the circuit.
- Circuit Breaker- A circuit breaker is a "self-repairing" fuse. It will open the circuit in the same fashion as a fuse. The surge creates heat the same way that a fuse is affected. When the surge subsides and the circuit cools down, the circuit breaker will reset and allow current to flow through the circuit. Typically circuit breakers do not need to be replaced.
- Fusible Link- A fusible link (fuse link or main link) is a short length of special, high temperature insulated wire that acts as a fuse. When an excessive electrical current passes through a fusible link, the thin gauge wire inside the link melts, creating an open to protect the circuit. To repair the circuit, the link must be replaced. Some newer type fusible links are housed in plug-in modules, which are simply replaced like a fuse, while older type fusible links must be cut and spliced if they melt
Always replace fuses, circuit breakers and fusible links with identically rated components. Under no circumstances should a protection device of higher or lower amperage rating be substituted.
Switches are used in electrical circuits to control current flow. The most common use of relays and switches is to open and close circuits between the battery and various electrical loads in a circuit. loads are rated according to the amount of amperage they can handle. All of the current that the controlled load uses flows through a switch. Using a switch with an amperage rating lower than what the circuit is rated for could overload and cause damage to the components located on that circuit. Relays
The underhood fuse and relay panel contains fuses, relays, flashers and fusible links
Relays are used to control high-current loads with lower currents. Since these some loads require a large amount of current, the thickness of the wire in the circuit is also greater. If a switch were used to control the circuit, all of the current required to power the high-current load would have to pass through the switch. From a design standpoint, relays are used to limit current through switches and reduce the amount of heavy gauge wiring in the vehicle.
Relays are constructed of a set of switch contacts and a small electro-magnetic coil. When current flow through the coil a magnetic field is created. This field causes the contacts to touch, in turn completing the high-current circuit. Typically, relays are constructed so that the secondary contacts are open when the relay is de-energized (turned off). Circuits where relays are used include, but are not limited to, the horns, headlights, starter motor, electric fuel pump, blower motor and cooling fan motor.
Relays are composed of a coil and a set of switch contacts. The large wires connect a high current power source to one side of the relay switch contacts and from the other side of the relay switch contacts to the load. The smaller wires connect a low current power source to the relay control coil and from the control coil to the control switch and then to ground.
Every electrical circuit must include a "load'' (something to consume voltage from the power source). Loads are resistances included in circuits to limit current flow. Loads are the components installed in circuits, such as headlights, wiper motors, door lock solenoids. Without a load, the battery would flow all of its energy through a circuit directly to ground. This is called a "dead-short to ground". The unchecked flow of electricity would cause a great amount of damage to the circuit by developing a tremendous amount of heat. Short circuits can develop sufficient heat to melt the insulation of surrounding wires, even reducing a multiple wire cable to a lump of plastic and copper.