Tip & How-To about Jeep Wrangler

How to wire a relay.

A relay is used when the load you want to switch draws more current than the switch available for the application. For instance, you want to install auxilliary/spot lights on your off road vehicle. The ignition switch may not be able to cope with the additional 15 or 20 Amps required. Enter the relay. It uses a small current to supply a large amount of power from the battery to where you need it.
On the bottom of the relay are numbers stamped next to the connecting tabs, they are wired as follows:

  • 30 - Connected to positive of the power source(battery). Put a fuse in line with this as close to the power source as possible.
  • 87 - Connected to load. This would be whatever you want to power ie fan, lights, electrical motor etc. The other side of the load is connected to earth(negative of the power source)
  • 87a - Anything connected to pin 30 is routed inside the relay to thispin when the relay is off. When the relay is switched on, this pin isdisconnected internally from 30.
  • 85 and 86 These pins are used to switch the relay. 85 isusually connected to earth. 86 is then connected to the activation switch and the otherside of the switch is then connected to your power source. (It does not matter which way round you connect these pins polarity wise, since between these 2 pins is a coil used to pull in the contact points and as long as they have power across them, the coil will activate.)
Below is a typical application. In this case to power a radiator fan.When wired as below the fan will work only with the ignition switchedon and the radiator hot. (Thermo switch - v - activated) This is not only suitable to Jeep but Dodge, Volkswagen, Ford, Chrysler, any vehicle as long as you keep to the basic configuration.
Let's get some air over that cooling system. Referring to the diagram:
  • i is the battery
  • ii is a suitable fuse(see below)
  • iii is a suitable switch or in this case the vehicle's ignition switch.
  • iv is the relay (Beware, there are different relay pinout configurations but the numbers stay the same)
  • v is the load (In this case the radiator fan)
  • vi is a thermostatic switch mounted on the radiator
When purchasing make sure firstly that the wire used is of the correct guage(thickness/current rating) for the given application. You dont want the wire melting because it is too thin and cannot handle the current. Find out how many amps the load will draw and add at least another 20% for reserve. The fuse rating should then be matched to the wire's capability since it prevents the wire and power supply (battery) from overload and fire.
If you wanted to wire your headlamps by this circuit, iii would be the high beam switch. The headlamp "on" switch should be wired between fuse ii and relay pin 30. Low beam is connected to pin 87A and high beam to pin 87 instead of the fan. The thermo switch would of course not be needed and can be replaced with a wire straight from pin 85 to earth.

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wiring multiple lights to one switch


I will suggest wiring a relay or even a number of relays into the circuit. Most switches can't handle high current flow so use the switch to operate the relays. You can wire in an almost countless number of lights without fear of burning out the switch. Draw out a diagram to be sure that you are staying within the operating limits of the relays, wires and connectors that you're using. You can also do the math to figure out which relays will work best for your application/requirements. If you'd like more help, please forward specifics about your components and what you're trying to accomplish and we'll build even more! :D

Jan 17, 2012 | Cars & Trucks

1 Answer

hi, i found a fog light in my shed, i want use it on my car for a reverce light..do i need to wire a relay??....& if so why?? thanks joe.


More than likely you will need to use a relay. Your reverse lights are rated for a particular amperage. The wiring, fuse and components are engineered for the amp draw. Adding an extra load like a high wattage fog lamp can cause the fuse to blow or damage the components/wiring to the reverse lights.

Relays work great for this type of application. They use a small amount of current to control a large amount of current. So adding a relay into the reverse light circuit will minimize the load draw on the circuit. It will then control either a fused power or ground (i prefer to wire them as ground side control so they aren't talking the brunt of the load which will make them last longer) that you run directly from the battery.

Oct 14, 2010 | 2003 Isuzu Rodeo

1 Answer

How do I change out the head light switch on 1992 geo storm


The headlight switch on this car may be changeable, but are you having a problem with the headlights working at all?

If so, then the following may be helpful:
---
REMOVAL & INSTALLATION Spectrum The headlight control switch is a 3 position, push type switch which is located at the left side of the instrument panel.
  1. Disconnect the negative battery cable. Remove the instrument cluster bezel retaining screw and the bezel.
  2. Disconnect the electrical connectors.
  3. Place the bezel on a bench and remove the 2 nuts securing the headlight control switch.
  4. Remove the headlight control switch.
  5. To install, reverse the removal procedures.
Storm The headlight control switch is located at the left hand side of the instrument panel on the meter hood.
  1. Disconnect the battery negative cable.
  2. Remove the meter hood.
  3. Remove the instrument cluster from the meter hood.
  4. Remove the 2 clips attaching headlight control harness.
  5. Remove the 4 screws attaching the headlight switch to the meter hood.
  6. Disconnect electrical connectors from the switch and remove the switch.
  7. Reverse procedure to install. Connect battery negative cable.
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SWITCHES & RELAYS Switches are used in electrical circuits to control the passage of current. The most common use is to open and close circuits between the battery and the various electric devices in the system. Switches are rated according to the amount of amperage they can handle. If a sufficient amperage rated switch is not used in a circuit, the switch could overload and cause damage. Fig. 1: The underhood fuse and relay panel usually contains fuses, relays, flashers and fusible links tcca6p02.jpg
Some electrical components which require a large amount of current to operate use a special switch called a relay. Since these circuits carry a large amount of current, the thickness of the wire in the circuit is also greater. If this large wire were connected from the load to the control switch, the switch would have to carry the high amperage load and the fairing or dash would be twice as large to accommodate the increased size of the wiring harness. To prevent these problems, a relay is used. Relays are composed of a coil and a set of contacts. When the coil has a current passed though it, a magnetic field is formed and this field causes the contacts to move together, completing the circuit. Most relays are normally open, preventing current from passing through the circuit, but they can take any electrical form depending on the job they are intended to do. Relays can be considered "remote control switches." They allow a smaller current to operate devices that require higher amperages. When a small current operates the coil, a larger current is allowed to pass by the contacts. Some common circuits which may use relays are the horn, headlights, starter, electric fuel pump and other high draw ciruits. Fig. 2: Relays are composed of a coil and a switch. These two components are linked together so that when one operates, the other operates at the same time. The large wires in the circuit are connected from the battery to one side of the relay switch (B+) and from the opposite side of the relay switch to the load (component). Smaller wires are connected from the relay coil to the control switch for the circuit and from the opposite side of the relay coil to ground tcca6g02.gif
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Sep 13, 2010 | 1992 Geo Storm

1 Answer

SV10 - V6 - Camry no power is getting to my fuel pump the fuse is ok and fuel pump works i can not find a fuel cut or fuel relay. A postion exists however its not in use. All I did was jack it up rotate the tires and dropped it kind hard off the jack Thanks Paul


SWITCHES & RELAYS Switches are used in electrical circuits to control the passage of current. The most common use is to open and close circuits between the battery and the various electric devices in the system. Switches are rated according to the amount of amperage they can handle. If a sufficient amperage rated switch is not used in a circuit, the switch could overload and cause damage. Fig. 1: The underhood fuse and relay panel usually contains fuses, relays, flashers and fusible links tcca6p02.jpg
Some electrical components which require a large amount of current to operate use a special switch called a relay. Since these circuits carry a large amount of current, the thickness of the wire in the circuit is also greater. If this large wire were connected from the load to the control switch, the switch would have to carry the high amperage load and the fairing or dash would be twice as large to accommodate the increased size of the wiring harness. To prevent these problems, a relay is used. Relays are composed of a coil and a set of contacts. When the coil has a current passed though it, a magnetic field is formed and this field causes the contacts to move together, completing the circuit. Most relays are normally open, preventing current from passing through the circuit, but they can take any electrical form depending on the job they are intended to do. Relays can be considered "remote control switches." They allow a smaller current to operate devices that require higher amperages. When a small current operates the coil, a larger current is allowed to pass by the contacts. Some common circuits which may use relays are the horn, headlights, starter, electric fuel pump and other high draw circuits. Fig. 2: Relays are composed of a coil and a switch. These two components are linked together so that when one operates, the other operates at the same time. The large wires in the circuit are connected from the battery to one side of the relay switch (B+) and from the opposite side of the relay switch to the load (component). Smaller wires are connected from the relay coil to the control switch for the circuit and from the opposite side of the relay coil to ground tcca6g02.gif
prev.gif next.gif --- I am not aware of an inertia switch on Toyota vehicles. I don't think it's like a ford. Look for a fusible link, fuse, or relay problem.

Jul 26, 2010 | 1996 Toyota Camry

1 Answer

dodge dakota selector switch and relay switch


A selector switch is what you use to turn on or off a circuit such as the lights or wipers. A relay switch is used by a circuit that has a large current draw and a relay uses a small source of current to control a large usage of current. Most fog lights use a relay to control the fog lights. You turn the fog light switch on (that is a selector switch) and the current from that circuit then activates a relay switch to let the larger current draw that the fog lights use go to the fog lights and you have light. A relay also controls if the fog lights are on when the bright lights are on. (on most cars if you turn the bright headlights on the fog lights will go out until you go back to the regular lights)

Hope that helps.
Good Luck

Jan 08, 2009 | 2001 Dodge Dakota

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