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Unread 11-13-2010, 03:31 AM   #1
92XJCowboy
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Basic Electrical

I am starting this thread because I have yet to see a good electrical thread that explains the dirty basics. Now that I am in school and learning this I would like to share the knowledge with fellow Jeepers. This is not a thread for complex theories and unnecessary ideas, Its to help the basic Jeeper understand why to wire his electric fan or fog lights in a certain way and why it works.

The book definition of electricity is the flow of electrons from atom to atom in a conductor. Electricity revolves around 3 basic things: Voltage, Current (Amps), and Resistance (Ohms)

Voltage is the Difference in charge at each end of the circuit. In other words its the pressure or push applied to the electrons. Measured in Volts.

Current is the movement of the electrons in the circuit. Current will Always find the path of least resistance. Measured in Amps

Resistance is the opposition of current flow. Basically its the friction in the circuit slowing down the electrons.

You can have Voltage w/o Current but you cannot have Current w/o Voltage. If you are still having trouble with how that works you can compare electricity to a garden hose. The water flowing through the hose is the Current while the pressure making the water move is the Voltage. If you put your thumb over the end then you have created a high Resistance and the current has been reduced.

There is a simple law that you should understand, Ohms Law. Ohms law states The Amperage (Current) in a circuit is directly proportional to the applied voltage and inversely proportional to the resistance. Simple right Here is is in plain easy to understand form:
-If the voltage goes up, the amperage will go up.
-If the voltage goes down, the amperage will go down.
-If the resistance goes up, the amperage will go down.
-If the resistance goes down, the amperage will go up.

Hopefully you understand things so far because there is more coming. I am going to try and make things as simple as possible and build slowly so it becomes as simple as possible to understand. For most of this I am going to use a light bulb as the load for simplicity.


Circuits consist of your power, wires (Red is Power, Black is Ground), load , and ground. With Jeeps your battery + is your power and your battery - is your ground. Say you were wiring your reverse lights up you wouldnt want to run a ground wire all the way back to the battery, This is why there is a ground strap from your battery to your body/engine block. Because of this you can hook up your ground to any bare metal on the body. Here you can see an extremely simple circuit.



In the next 2 pictures I have added a switch and a fuse and shown what the switch does.





A Fuse is installed in your circuit as a safety against over powering an item which can cause damage and/or fire. It is a thin piece of metal that will melt (pop) at a certain temperature (The more electrons you try and shove through an area the hotter it will get). Most of the time what will cause the fuse to blow is a short in the circuit. A Short is any path that the electricity can take that leads it away from the desired location, One example would be a bare wire rubbing against bare metal. A short can exist in a system and still power your device, It will act as a drain on the battery if you have an improper or lack of a fuse. You can see in the picture how a short can divert power away from your device yet still have enough for it to be powered.




The closer to the power source you mount the fuse the better as it can protect more of your circuit and help keep your battery from draining. In the next picture you can see a fuse that has blown.



There are 3 basic types of Circuits: Series, Parallel, and Series-Parallel.

Series is a circuit in which the power only has one path to travel. Say you have 5 switches in a circuit, If you turn one off then power to the entire circuit following the switch is cut off.





Parallel is a circuit in which there are multiple paths for the power to travel. If you have 3 switches in a parallel circuit they do not effect each other if turned off or on. This would be good for an electric fan if you were to use a manual switch and a thermostat switch.





A Series-Parallel circuit is just a combo of both. You can have a few switches wired in parallel and have a single switch wired in series that shuts them all off.

Now you have been through the most basic of wiring I will go a little more complicated and introduce you to Relays.

A Relay is an electromagnetic switch. It allows you to use a small amount of current to control a large amount of current. For example, Your starter is triggered via relay. If you didnt use that relay you would need to run a rather large and powerful wire into your steering column which creates a fire hazard as well as a space issue.

In a relay you have 5 terminals: 85, 86, 87, 87a, and 30. 85 and 86 control your electro-magnet. You run your switch power into pin 86 and run a ground from 85. You run your battery power into 30. 87 and 87a are what you wire your device to. Most of the time you are going to use 87 as your supply.

In the picture I have shown everything wired. The angled arm that goes from 30 to 87a in the first picture and from 30 to 87 in the second is just a switch that is moved by the electro magnet.





In the next few pictures I have taken the original circuit from earlier and added a relay. Yes it does somewhat complicate the wiring but its a safer and better way to wire in new components.





One of the cool things about relays is that you can trigger so many things with one switch. If you didn't have relays for your starting system you would have a dash full of switches that you would need to fiddle with every time you went to start your Jeep. One turn of the key to start automatically turns everything like your radio and cigarette lighter off at the same time it turns your fuel pump on and powers on your ECM, Starter, Spark plugs, and Alternator.





You can also control relays using the ground instead of power. It is the ultimate spark/arc proof way to wire a switch in your dash. Its just a matter of putting the switch between the ground and terminal 86.

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Unread 11-13-2010, 06:17 AM   #2
compcrasher86
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Very good. Everything looks right as it should be. Im an EE student up at RIT so I will appreciate this on the behalf of others who are new to wiring. I always thought it would be nice to have a resource thread like this. I might make a couple diagrams when I get home to add on to yours but you covered all the basics

Its worth noting to those who didnt read all of it or didnt completely get the concept... you do not have to run a negative wire all the way back to your battery. Because the Jeep is made of metal, it has a wonderful ability to conduct electricity. How can this benefit me, you may ask yourself? Well, the battery negative terminal is directly connected to the Jeep's metal as well so almost anywhere you can get a good connection to the body metal on your Jeep you'll get a good ground!

and to add a bit on relays:

Theyre really efficient and useful in the automotive environment in several different ways. By using one you can keep your higher powered wires out of the dashboard. Most relays will only draw .25 amps at most so you can use thin (I use 18ga personally) wire to power them from the switches inside. Plus, you can be creative with the source power. Heres an example: In my XJ I power the switches off of the cigarette lighter. The cigarette lighter only has power when the key is on. Basically my switches only provide power to the relays when the key is on so if I shut off my key my lights will turn off as well. Pretty convenient.
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Unread 11-13-2010, 10:11 AM   #3
Jerry Bransford
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Nice post, that will be very helpful to those not up on electrical circuits. In fact, I will make it a part of our FAQ section later this weekend if you don't mind.

Compcrasher added some nice comments too, especially on the Jeep's body and tub being able to act as the negative lead for most circuits. About the only time the tub or chassis cannot be used for the negative return connection to the battery is for a winch which absolutely must have its negative lead connected to the battery's negative post. Merely grounding the winch's negative lead to the chassis could burn up a whole lot of little tiny ground connections between the chassis and battery if the winch were used on a heavy pull that can draw more than 400 amps.
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Unread 11-13-2010, 11:27 AM   #4
92XJCowboy
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Quote:
Originally Posted by compcrasher86 View Post
Very good. Everything looks right as it should be. Im an EE student up at RIT so I will appreciate this on the behalf of others who are new to wiring. I always thought it would be nice to have a resource thread like this. I might make a couple diagrams when I get home to add on to yours but you covered all the basics
Anything you can add would be great.

Quote:
Originally Posted by Jerry Bransford View Post
Nice post, that will be very helpful to those not up on electrical circuits. In fact, I will make it a part of our FAQ section later this weekend if you don't mind.
That would be great Jerry thanks.
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Unread 11-13-2010, 01:34 PM   #5
ChiliPalmer
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Awesome job!

I did find one simple error. In the first paragraph regarding relays you mention "You run your switch power into pin 86 and run a ground from 86." Whoops


And for those reading this make sure you check out Sirgcal's writeup in the sticky section, inside you'll find a link to a calculator for OHMS law and how much current lights will need. Pretty cool tool if you're doing a lot of wiring.
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Unread 11-13-2010, 11:38 PM   #6
92XJCowboy
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Quote:
Originally Posted by ChiliPalmer View Post
Awesome job!

I did find one simple error. In the first paragraph regarding relays you mention "You run your switch power into pin 86 and run a ground from 86." Whoops


And for those reading this make sure you check out Sirgcal's writeup in the sticky section, inside you'll find a link to a calculator for OHMS law and how much current lights will need. Pretty cool tool if you're doing a lot of wiring.
Whoops is right thanks for pointing that out.
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Unread 04-16-2011, 10:07 PM   #7
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Quote:
If the voltage goes up, the amperage will go up.
-If the voltage goes down, the amperage will go down.
-If the resistance goes up, the amperage will go down.
-If the resistance goes down, the amperage will go up.
I = E/R so, high voltage doesn't always carry high current... inversely speaking.. it takes resistance to make that amperage or current.. you get hit by 1000 volts with no amperage, you walk away.. you get hit by 1000 volts and 1@, you may not walk away.. depending on your resistance to ground, R= E/I .. so, with the wrong combo, you get fried.. Lightning is a perfect example.. 1000's of volts and most walk away.. yet touch a power line grounded, and you'll be carried away..
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Unread 08-29-2011, 05:11 PM   #8
My83andMe
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I just gatta say thank you for the thread... I'm trying to figure out my ignition off power draw issue and being I'm clueless as to anything ectrical but slowly learning (both the easy and unfortunately the hard ways) this thread explains what tends to just fly over my head its much appriciated.
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I thank you and believe me my Jeep definatly thanks you cus otherwise I'd be turning a wrench with out a clue. :)
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