Understanding automotive relays wiring diagram

Every circuit added to a modern car should be run through an automotive relay. The factory wiring in modern cars is light gauge, and is not designed for additional loads. A relay can be used to power a new circuit with very little added current draw on the original wiring.

Using a relay can also shorten the distance that high-current wiring needs to run. Connect relay terminal 87 to the vehicle body or battery negative terminal. Use a piece of gauge primary wire with a solder-less female spade connector on one end, and a solder-less ring terminal on the other. Connect relay terminal 85 to an automotive circuit breaker.

Connect the circuit breaker's other terminal to the battery's positive terminal. Use primary wire that's large enough to handle the current load of the new device.

Connect relay terminal 86 to the device that needs power. Use the same gauge wire as that used for terminal Run an gauge primary wire to a switch in the driver's area.

Power the switch from a fused circuit inside the vehicle. Connect the wire to relay terminal 30 with a solder-less connector. This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information. To submit your questions or ideas, or to simply learn more about It Still Works, contact us.

How to Wire an Automotive Relay by K. Step 1 Connect relay terminal 87 to the vehicle body or battery negative terminal. Step 2 Connect relay terminal 85 to an automotive circuit breaker. Step 3 Connect relay terminal 86 to the device that needs power. Items you will need Solder-less connectors Toggle switch Inline automotive circuit breaker Primary wire. About the Author This article was written by the It Still Works team, copy edited and fact checked through a multi-point auditing system, in efforts to ensure our readers only receive the best information.So, how to read car wiring diagrams?

A car wiring diagram is a map. To read it, identify the circuit in question and starting at its power source, follow it to ground. Use the legend to understand what each symbol on the circuit means. A wiring circuit is so called because the wiring must make a complete circle, any break in this circle, causes a fault. Power leaves the positive side of the car battery through the power cables and is always actively looking for the shortest possible return path to the negative side of the car battery.

Power is battery voltage and in any circuit the path to the load from battery positive may be described as the power side of the circuit. As you know, voltage loves to travel through any metal, and not just the metal within wires. The return path after the load is known as the ground side of a circuit. The function of a relay is to control a high amp circuit like a starter motor or head lights using a low amp switch circuit.

Running high amps through a small switch would cause the switch to burn out and fail, possibly starting a fire.

PLC Training - Reading electrical wiring diagrams and understanding schematic symbols

Relays are common in circuits and also housed within control units. A relay is a electromagnetic switch, it has two separate circuits, a Control circuit and a Load circuit.

This causes the coil of the relay to become magnetic, which pulls the movable armature within the relay, closed. When closed open in the above diagramit allows power travel from the battery to the light.

Through the 30 and 87 pins. When the switch is turned off, battery disconnected the coil is no longer magnetic and the spring loaded movable armature returns to open default position. The starter circuit relay in the pic above operates in an identical fashion. By turning the ignition switch to start, voltage flows through pin 86 and grounds at This magnetises the coil which in turn causes the armature pin 30 to 87 to close completing the load side circuit, and the engine cranks.

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Modern cars as you know are packed with control modules. Pre-computer classic cars have a simple wiring circuit — for example, pressing a switch sends power through a wire, to a window motor and the window moves. Modern cars handle it a little differently — pressing a switch, sends a signal through a wire to a control unit computerwhich in turn sends power to the window motor. The control unit or controller will only send power to the window motor if certain pre-programmed conditions are met.

Of course the window may not move for other reasons, the control unit may be faulty, or software needs to be updated or re-flashed, motor faulty etc. So why did they go and make things more complicated and expensive to fix?

Well, control units do offer significant advantages, some of which include:.

understanding automotive relays wiring diagram

All control units are connected to each other via a twin twisted pair of wires, the communication system is know as CAN controller area network. It will typically show a set of symbols and a brief description. Tip : Some diagrams are easier to understand than others, but having the wrong wiring diagram can catch out even the pros.

To avoid frustration, be sure that your wiring diagram is correct for your vehicle. Wiring diagrams were traditionally printed in book form, diagrams are big as you know, to fit them all on one page would make them unreadable.

The solution — a number at the end of each circuit indicated the page on which the rest of the circuit diagram was continued. Other solutions include showing just one systems wiring circuit to a page, for example, just showing the wiring diagram for the headlights.

This works pretty well and was carried over to the digital age. Digital wiring diagrams are a lot more efficient and easier to use, so if possible, always opt for digital schematics. The diagram below is a basic car light circuit, at first sight it might look complicated, but as you understand the flow, it will become clear. Remember, battery power voltage at the top of the page is trying to get to the ground supply at the bottom of the diagram.The electrical system of a car is a closed circuit with an independent power source the battery.

It operates on a small fraction of the power of a household circuit. Current flows along a single cable from the battery to the component being powered, and back to the battery through the car's metal body.

The body is connected to the earth terminal of the battery by a thick cable. This type of circuit is called an earth-return system any part of it connected to the car body is said to be earthed. The strength of the current is measured in amperes amps ; the pressure that drives it round the circuit is called voltage volts.

Modern cars have a 12 volt battery. If the battery voltage drops, less current flows, and eventually there is not enough to make the components work. The extent to which a wire resists the flow of current is called resistanceand is measured in ohms.

Thin wires conduct less easily than thick ones, because there is less room for the electrons to travel through.

The energy needed to push current through a resistance is transformed into heat. This can be useful, for example in the very thin filament of a light bulb, which glows white hot.

However, a component with a high current consumption must not be connected using wires which are too thin, or the wires will overheat, blow a fuseor burn out. All the electrical units of measurement are interrelated: a pressure of 1 volt causes a current of 1 amp to flow through a resistance of 1 ohm.

Volts divided by ohms equal amps. For example, a light bulb with a resistance of 3 ohms, in a 12 volt system, consumes 4 amps. Often the power consumption of a component will be stated in wattswhich are found by multiplying amps and volts. The lamp in the example consumes 48 watts. Electricity flows from a battery in one direction only, and some components work only if the flow through them is in the correct direction.

This acceptance of a one-way flow is called polarity. This is called a negative earth system, and when buying an electrical accessory a radio, for example check that it is of a type suitable for your car's system. Fitting a radio with the incorrect polarity will damage the set, but most car radios have an external switch for setting the polarity to suit that of the car.

Switch to the correct setting before fitting.To begin understanding how to read and understand electrical circuit diagrams, take our basic circuit and draw it out as it would physically be wired.

We show our AC power source on the left with L1 and N coming out of it, our switch to the top, and our light to the left. Power comes out of L2 to the switch, which when open, breaks the circuit preventing current flow and when closed, ties the left and the right terminals of the switch together, allowing current flow. The switch is connected to the light, then there is a neutral or return wire back to the power supply.

Very quickly, this simple diagram would turn into a great big mess. If you notice our "Getting Started Wiring Guide" omitted half the trainer. If we had represented a wiring example of the entire trainer in this manner, you would not be able to follow it. So to simplify this, your power wires, in this case L1 and N, run vertically down the page.

understanding automotive relays wiring diagram

As you draw out these circuits the diagrams begin to take the shape of a ladder which is where ladder diagrams get their name. Usually, if it is three phase then L1, L2, and L3 run down the left side of the page and if there is a neutral N then it runs down the right side of the page.

In single phase diagrams L1 will run down the left side of the page and N or L2 will run down the right side of the page. The power source, if external to the drawings, is usually not shown. This will become clearer when you begin working with our control panel sample wiring diagrams in the exercises below. The next key advantage of ladder wiring diagrams over drawing circuits is the way they are physically laid out so that they are indexable, meaning device names can give you the page and rung number that the device can be found on in the ladder wiring diagrams.

Also devices that may span multiple locations in a drawing such as a relay coil and its contacts can easily be cross referenced. For example, study the diagram to the right. Our power source L1 and N are running vertically as you have learned and now you have added rung numbers to the left of the ladder for reference.

These usually increment by one as you go down the page and may incorporate the page number into the rung number. So, in this case, the three probably represents page 3, then you are looking at Rung 01 and Everyone does it a little bit different but once you understand the basics it only takes a few minutes of examining most sets or drawings to follow them. That means it is on Rungit is a switch SWand usually there will be a number that increments by one from left to right.

So if we had a second switch it would be labeled SW2. The switch would be labeled SW1 in the field.

How to analyze any schematic for automotive simplified to detail for beginners part two

That way when someone looks at the switch, they know exactly where to find it in the wiring diagram. Next you see a label "". This is the wire number of the wire that connects the switch to the relay and it should be labeled as such on each end of the wire and in any junctions that connects it. This way if someone sees this wire number, they know to go find Rung then find the first connection point. Also note that the wire to the left of the switch is not labeled because it is connected to L1 which is labeled at the top.

With very few exceptions, connections that are physically connected, such as L1 is to the float switch, should keep the same wire label, in this case L1, throughout the drawings.

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Now you are at the relay coil. This is an important concept to grasp. It is not the entire relay that you would physically hold in your hand.

It is only the coil that, when energized, pulls in the relay contacts. Being able to find its contacts is a key advantage of ladder wiring diagrams.A relay is basically a switch but not like a switch that's on a wall. A wall switch relies on someone to flip it which will then control a light or some other type load. A relay is switched by electrical power and not a human. This is done by energizing a coil which is internal to the relay and by energizing the coil, the relay changes state just like a wall switch would.

Therefore when you energize a relay, you are switching circuits off and on. Relays have many purposes and are used in a variety of ways such as electronic circuit boards, machines, appliances, automobiles and the list can go on. The main purpose of a relay is to switch electrical circuits off and on at given times and allow circuits to be automated.

A great advantage with relays is the ability to switch many different circuits of different voltage types all at once by using the same relay.

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Wiring Relays Although relays come in a huge variety of designs, shapes and sizes, They all basically work with the same concept. I'm going to be covering some industrial relay logic and the images you see here are some of the most common types used for industrial controls also called machine controls.

These images show a square 3-pole relay and it's socket on the left and a round 2-pole relay and it's socket on the right. The socket is used to connect your wires to the relay. This particular relay with 3-poles means you have 3 separate switches or what we'll call contacts.

And So On. The square relay pinout shows how the relay socket is configured for wiring. This pinout image is only a 2-pole diagram for room on the page purposes, but you can get the picture here with this one since a 3-pole will just have 1 more set of contacts. As you can see, there is absolutely no difference between the square type and the round type other than the ratings on the relay.

Otherwise they work exactly the same. See my Switch Terminology Page for more on contact arrangements if you need to. By looking at the diagram below we can go through the basic concept of a relay and how they operate. This diagram will show you how simple it is to control motors, lights, valves, other relays and any type load you want.Mechanics use car wiring diagrams, sometimes referred to as schematics, to show them how automotive manufacturers construct circuits.

In fact, a typical service manual will contain dozens of these schematics that can help with proper diagnosis and repair. On this page is a how to video some coworkers and I put together. It explains how to find specific automobile wiring diagrams, but more importantly tips on using them to fix complex problems.

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This video is good stuff and worth 6 minutes of your time. Although the video views continue to climb we still got a few thumbs down. However I tried to supply unique and helpful information. One guy was upset, because I mentioned using a test light instead of a meter. First, not everybody has a meter at home.

Now lets get back to the diagram issues. There are electrical symbols posted on the schematic that will indicate the color of the wire, its thickness or size and other important details about that particular circuit such as connector locations. Identifying the color of the wire is important for accurate diagnosis. If you test the wrong wire you will go down the wrong branch of the tree chart. The standard labeling system will use the first letter to indicate the base color, and the second letter to indicate the stripe color.

An example would be the letters OB. This represents an orange colored wire with a black tracer stripe. RB is red with a black tracer. Wire repair diagrams can become quite complex.

understanding automotive relays wiring diagram

To avoid this, most troubleshooting manuals will illustrate only one distinct system or circuit at a time. A horn circuit or turn signal circuit each have a separate distinct electrical schematic. Keep in mind that electrical symbols are not always standardized throughout the automotive industry. Different manufacturers may have different methods of representing certain components particularly the less common ones. Always refer to the symbol reference charts on the wire schematics.

However, some car makers list these in the beginning of the electrical section in many professional manuals. In this video I share the method my electrical instructor taught me. He was an evil genius and his brain flowed like electrons.

Most auto mechanics have learned a different method. I think, what is more important is to use a standard procedure and follow it religiously for each electric diagnosis.

Sticking to a routine helps you find problems faster. Find 3 more instructional videos about how to use online auto service manuals to fix cars right the first time. This next link takes you to my page about online factory auto repair guides. Do you require one on one help with your particular electrical problems?

On this website automobile repair help is always available for you. Testing individual electronic components is not only a valuable skill, but a big part of fixing electrical problems on cars.

In my college training classes we sat down with bread boards and learned how to diagnose and repair individual components. The video has the same goals. You learn about the tools and the proper equipment required for automotive electrical tasks, but more importantly how to decipher the test results. In my opinion it is a clear and concise video with enough attention to detail so the enthusiast understands what this stuff means to the efficient repair of automotive electrical circuits.

Find out what else is available on this auto repair website on the Homepage for YouFixCars. You can also learn more about the car mechanic that created this information portal.When wiring anything in your vehicle that draws heavy current such as high powered offroad lights or audio amplifiers, there are a few things to consider. Number one, make sure you use wire that is rated for the amperage that the accessories is going to pull. It is always better to have wire that is OVER rated rather than wire that is not rated high enough.

If wire is used that is not rated to handle the current that your accessory will pull, the result could be overheated wires that could melt the insulation or the electrical plugs found throughout your vehicle see image belowcausing a short or worse yet it could result in a fire. If you know how much current your accessory will draw you can determine what gauge wire is appropriate for your application.

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Personally I like to use wire that far exceeds the current draw of my accessory. That way there is no question as to whether the wire is rated high enough or not.

If this approach is taken, it is very wise to place a fuse at the battery end as close to the battery as possible. Most wire in a vehicle, if shorted out, will burn up before the battery overheats and possibly explodes. If wire that is over-rated for vehicle use is used and a short occurs, a short will most likely result in damage to the vehicle of some sort unless a fuse is put in line as close to the battery as possible.

With the fuse there, in the case of a dead short, the fuse will burn out first before any damage could occur. The second important thing to consider when adding accessories is to determine where you will get your power.

Many people will consider tapping into the hot wire of an existing circuit using something called a T-tap or quick slide connector, which are designed specifically for tapping into an existing wire.

This is not always a good idea for several reasons. First and foremost, tapping into an existing circuit puts additional load on that circuit. The additional load placed on a circuit or wire may exceed the limits of those wires, connectors and fuse. Overloading a circuit will do one of two things. First, it may blow a fuse. So people will sometimes place a larger fuse in the fuse block to handle the extra load on that circuit.

The fuse may hold but the resulting extra current may be more that the wire is rated for creating heat that can melt wires and connectors and start fires! The connector to the right was overloaded and fused two adjacent terminals together, causing a short the blew the vehicles main fuse.

Before the fuse blew the connector actually started to burn.

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The wire that carried the extra load also had melted its insulation and in places was exposed. Luckily for the owner of this vehicle, it did not result in a fire but in many cases it does. With accessories that pull a lot of power it is always better to get your power directly from the batteries positive terminal rather than tapping into the existing fuse block or wiring harness. In most cases the vehicles existing fuse blocks, wires and connectors are not rated to handle the additional load of high powered accessories such as offroad lights and amplifiers.

If you are the kind of person that likes to add all kind of goodies to your vehicle it might be worth installing an additional fuse block that handles non-critical items like offroad lights, CB radios, power inverters, audio equipment, etc.

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This additional block can then be powered by a heavy duty wire capable of carrying the current required of all the accessories on the block. Be sure to fuse the block at the battery. In almost every case where high current is required, the switch you will use to turn on the power should not handle the load because most switches are not designed to handle higher amps.

The job of switching the power is better left to a relay.


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