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Discussion Starter #1 (Edited)
The Electrical System ExplainedBy Gil "usmcdoc14"
[ PART 1 ] [ PART 2 ] [ PART 3 ]
The first modification done to most any Jeep typically involves the electrical system. Be it as complicated as a winch, or as simple as a set of off-road lights, and they are done by everyone, to almost every vehicle. But as deceptively simple as most electrical modifications may seem, they are also the most dangerous, due to the common mistakes and lack of attention to detail when doing the installation. What you will be getting here today is not only a primer in electrical upgrades and installation, but a valuable lesson in what the most common and dangerous mistakes are.
So lets start at the beginning:
Each of these points will be simplified not to "dumb it down" but to give you the basic understanding of your electrical system. Each aspect will be discussed as to its function and importance in more detail as we go along.
Your JK is a 12 volt, direct current, negative ground system that is powered by an alternator and battery system. Yes, I know an alternator and battery both have above 12 volts when charging or fully charged (around 14 volts), but we are keeping some things basic and this is how accessories are sold. Its is direct current (DC), that means the negative is the negative, positive is positive and they do not switch back and forth like alternating current (like your house). A negative ground system means that the chassis and body are wired to the negative post of the battery and the alternators negative is though its case to the engine/frame. All the positive power is ran in wires and most all modern cars are negative ground.
What are Volts, Watts, Amps and Ohms, and why do I care?
Now you may be thinking "I don't need to know this, my stuff comes from the factory or in the box already wired". Well you would be wrong, or better yet, a lot of companies are completely wrong and send substandard wiring. But you would be oblivious to this because you may not be educated on automotive electrical systems.
Its best to be well educated instead of stuck on the side of the road or trail on fire.
Think of electrons like water, and your battery/alternator as a water tank or pump with pipes. It makes it a little easier to visualize.
Volts Volts (voltage) is like water pressure in the tank or from a pump. (battery/alternator) It can be constant (vehicle running) or can gradually go down (battery only) just like the pressure in a tank unless there is something to replenish it (alternator).
Amps Amps (amperage) is the amount of water that can or is going through the pipes at a given time. So if you have a bigger pipe more water can flow through with out doing causing damage. If you are running more amps you are going to need a wire big enough to handle it.
Watts Watts (wattage) is the amount of work the water can or is doing. For example the watts of a light bulb.
Ohms And lastly, ohms. Although you will not have much use for them in most simple wiring it is best to understand what it is anyway. Ohms is the amount of resistance caused by the pipes, what is attached to them or what is in them. If you make a pipe longer, smaller, put your thumb over the end or put rocks inside it (impurities), then there is more resistance to overcome to get the same flow. The same thing goes for how big wires are or what they are made from of.
How these terms apply to you is it will allow allows you to safely select wires, switches, relays and other items based on the needs of what you plan on adding to your Jeep. For example, or better yet, the best example, would be off road lights. These being THE most common and first upgrade that most people do an off-road vehicle. On that same note it is also the one that is often done half-assed and dangerously. The danger begins with people misunderstanding the requirements of the lights. They see that they are installing a 55w light and that's about where it ends. They have no idea what the correct wire size, fuse size or switch is unless its included with the product. If you get some cheap chicom knock-off light you can pretty much bet the wire/fuse/switch will be substandard. But now that you understand the basic terms of automotive electricity you can figure out exactly what you need!
So you know that you have a 55watt light, 55watts is how much work the light is going to do. You know its 12volt because the box or bulb says so, but how do you figure out what amperage fuse, switch or wire to run? This is what we will cover next.
Basic math Everything revolves around you knowing numbers, you can't figure the wire, fuse, switch or anything until you know what your electrical item requires in order to work. Luckily most products will list the maximum amp draw in the owners manual or online. Too bad they do not do that with your common off-road lights, Luckily that is quite easy to figure out.
Wattage will always be listed, even if you have to just look at the bulb. Your amp requirements are figured really simple.
Amps = watts, divided by volts.
So you have two 55 watt lights on a 12 volt system. 110 (55x2) divided by 12 = 9.17. Now knowing this, you can start choosing the rest of your electrical system to safely match. To do this you should just follow these steps.
Find the amp draw of what you want to wire.
Choose a wire that is made to function at or above the amp draw of the accessory.
Fuse the wire to less than its maximum amperage.
Choosing wireFor automotive use we will be working with stranded wire instead of the solid wire like you would find in your house. Solid wire (made of a single solid wire) flows electricity the same but it just does not handle vibration well and will eventually fail. You want to use automotive or marine grade wire. Its muti-strand and it's protective coating will be resistant to UV light, oils, abrasion and the other hazards of being in a jeep. Do not go and use lamp cord, com wire, speaker wire or any of the junk that people use that is NOT DESIGNED to be safe in a vehicle.
Do you have any idea how many cars I have fixed that were wired up with lamp cord?
Anyway, You can pick up wire from your local auto parts store or boat/marine shop. Myself? I prefer to use tinned wire and order it online from boating places. Tinned wire takes longer to corrode and getting it online in bulk saves a lot of money over the little 25' spools you get at a retail store. But any automotive or marine grade wire will usually suit your needs just fine.
Wire is measure in gauge or how thick the wire bundle is. This is measured in numbers like lead shot or needles where the smaller the number the bigger the wire cross section is. 10ga being smaller than 2ga and 00ga being much larger than 24ga. Your wire gauge will be dictated by the amps you plan on running through it and how long it needs to be. People will go and figure the amps but fail to take into account how long the wire run is. The longer the run, the more resistance, the more voltage drop, the more heat and the bigger gauge wire you need. The complete run is figured from the battery to the accessory and then back.
Each company has rating for its own wire and no one else's. For EXACT max rating of the wire you need to see the data sheet ON that brand/company wire. Boat/marine have stricter guidelines on wire than SAE/automotive so using their wire will add a measure of safety as well. You will want to base your choice on the continuous amp draw of the accessory.
Here is a rough chart for a rough go-by to help you out.
But you can ALWAYS go overkill on the wire, you can ALWAYS use larger than what you need or rated. This allows you to correctly fuse and make sure that your under the max amps of the wire. Always choose a wire rated at or ABOVE what your accessory requires. That chart and most companies list the max amps at the continuous draw with the wire by itself cooling in the open air. Wires get heated under normal use by the electricity running through it, but with too much amperage the heat melts insulation, this causes a short and hopefully not a fire. So when you have a bunch of wires tight together or in a loom you may wish to up the gauge just for that reason alone. Then you add the heat from under your hood and you are cutting it kinda close with the point of failure of the wire. Take these into consideration when choosing wire size.
Remember Always fuse the wire, not the accessory !! This means to make sure your fuse is less amps than what the max amps of your wire. Yes, your accessory may require a 20a fuse, but if your wire will catch fire at 18a you need to fuse it before that point. The fuse needs to be your weak point of failure at all times.
Choosing your fuseNow that you know your amp draw and the correct gauge wire you will need to fuse it correctly. Luckily, that is the easy part. You just make sure the fuse will pop before the wires failure point. You also want the fuse as close to the battery as possible so there is as little unprotected wire as possible. You do not want the fuse far away from the battery because you do not want the chance of a short before the fuse, defeating the whole reason a fuse is there. Again, your fuse should ALWAYS be your weak point.
That's it, almost.
You will need to figure the performance needs for your accessory.
A common automotive fuse is set to fail at a set amp, this works fine, unless your item requires something different. If your accessory is a high amp item, say above 30a, a common automotive fuse may not be high enough. Or if your accessory has a high amp draw only at start up you may require a slow acting fuse that still protect the wire at its continuous rating but allow the high start up amp. An example would be an HID light or a compressor that has a peak draw when it first starts up.
Or what if you don't want to keep buying fuses or have an item above a common rating? In that case you would run a circuit breaker. These can be automatically resetting types (resets when the power is turned off) or manual reset (throw a lever or push a button) and can vary in size from a 2.5a to 300a and above.
I myself like to run manual reset circuit breakers because I want to know WHY my circuit breaker tripped and solve that problem before I reset it.
Now as mentioned before, what the type and brand of fuse will dictate when it blows. The amperage at which fuses actually blow, and circuit breakers actually trip, are sometimes considerably higher than their nominal ratings. SEA, Maxi, ATO and AGC fuses, and most circuit breakers, blow or trip at about 130% of their rating. ANL fuses blow from 140% to as high as 266% of their rating.
You NEED to take this into account when fusing a high amp system, but luckily, the information is easy to find from the company website for the manufacturer of the fusing system.
You will also need to choose a holder or fuse block. Fuse holders work great for a single item or when the total amperage of all your individual items will exceed the capacity of the fuse block. They are also very easy to waterproof or come waterproof out of the box.
Here are a pair, now they are rated the same amperage but you notice the different size. Its your choice as to what one you want to run, but the smaller one will make your jeep fused alike.
This is your typical fuse block from an average auto part store. Its simple and reliable as long as you read what the maximum amperage for the entire block is. If you want more high end or sealed blocks you can stop by any boating or marine shop.
Here are some examples of fuses and circuit breakers, the smaller fuses being what is factory installed in your JK:
Choosing your switchingYou got your accessory, you got the correct wire, you got the correct fuse, so how are you going to turn it all on and off?
Just a simple switch is easy enough. Make sure the switch can handle the max amp of the accessory and you are good to go.
Even a not so simple switch is easy, once again you just make sure the switch can handle the amps, follow the wire diagram on the back and you are ready to rock.
You can switch either the positive or the ground. Most of the time if not all you switch the positive because it requires less wiring. The positive wire goes to the switch, then from the switch to the accessory. The ground from the accessory go goes right to the frame or body right next to it. Switching the ground requires a wire from the battery to the accessory, and then from the accessory all the way back to the switch and THEN to a ground. But either way works depending on what your requirements are because there are at times, benefits to a switched ground like when you need an item to turn on if the switch fails.
What limits us in running "just" a switch is the same problem that automotive manufacturers figured out years ago.
When you have 5 or 6 high amp items that need to be turned on/off where do you run all that thick wire? What if you have a accessory with a amp draw higher than your switch is rated? how do you use it?
You run a relay.
A relay is, in its basic terms, a electromagnetic switch that is turned on and off by a low amp power. You apply power to the relay, the electromagnet in the relay causes the contacts to complete a circuit and the current flows to your accessory. This allows you to turn on a high amp item using a very small or low amp switch using small gauge wire.
Could you imagine running your starter wire all the way to a huge switch on your steering column and then all the way back? Along with controls for wipers, blinkers and lights? You would have a steering column that would be huge. That's why car makers use relays.
The great thing about running relays are:
Smaller wiring.
Smaller switches.
Safer wire routing as only low amp wire is ran though the firewall into the cab.
Safer wiring as there is less wire required for the entire run of the circuit.
Smaller gauge wire required for the accessory as the run of the circuit is shorter.
Can handle higher amps than just a simple switch.
Can be switched in multiple ways (more on this in a bit).
The bad things are:
More wire.
Can be confusing
Not as simple
Although there is nothing wrong with just running a fused wire through a switch to your accessory, I prefer to have mine run with a relay to keep the wire diameter in the passenger compartment to a minimum. I also like to run switches that are smaller but still over rated for the requirements of the relay.
Another great thing about a relay is it does not care what end of a circuit it completes, positive or negative. Power is applied and it electromagnetically closes, what goes through its contacts does not matter. This can be very useful for turning one accessory on with multiple ways. Examples of this include:
Additional reverse lights that you want turned on by the factory reverse lights and/or a switch.
Cooling fans you want controlled by a thermostatic switch and/or a dash switch.
You can not easily run multiple positive power sources to the same item with multiple switches. What will happen is either it will double the volts and fry something or it will flow back through a switch and fry something. You can do it with some more complex electrical that never works out for me or you can do it quite simply and switch the ground with relays.
You run your normal fused positive wire directly to the accessory and you use multiple relays or switches (depending on your choice of switch) to control when the accessory is grounded. When its grounded it completes the circuit and turns on! Use as many relays as you need switches.
We will cover wiring a relay a little bit later, its not hard, trust me.
But how do I connect everything?
I am going to cover the good or best connectors here. Sorry, but I have no time for substandard connections. Electrical tape may work great in your house but it has no place at all in a jeep. The same goes for some other utterly retarded connections I see all the time. While we are here on this rant, lets cover some of the most horrible ideas to be used in automotive electrical upgrades.
Wire nuts, WIRE NUTS !!!??? Who ever thinks that a wire nut belongs in a vehicle needs to be force fed a box of them.
T-splices, scotch connectors, inline splices or whatever you would like to call them.
Those things are the most horrible invention ever created. I don't care if it came with the accessory from the factory with one. Just throw it away, it is the lazy mans electrical salvation but at the same time will make you work harder in the end. No cutting, no twisting, no solder, you just slide it on and squeeze with pliers. It also offers no protection from the elements, in fact it leaves the wire nice and open to corrosion. It is also inherently dangerous, it allows you to tap into an already existing circuit to "tap" into its power. That circuit already has a job, a amp draw and a power requirement and there you are trying to suck more power from it and exceed its operating parameters.
Walk away from the T-splices and do things right.
Doing connections rightThe most common and easy way to do a connection is using crimp style connections. They work well, are simple, anyone can do them and the will not fail if done correctly.
The problem is people do not do them correctly nor seal them when done. Get a quality crimper instead of a pair of vice grips, also use either crimp connectors that have a heat shrink media built in or cover the connection with heat shrink tubing.
If you can find them, use waterproof removable connectors such as weatherpac. These will allow you to have a connection that is completely waterproof but also easy to take apart should you ever need to.
I own huge amounts of adhesive lined heat shrink tubing, the adhesive melts when you heat the tube to shrink it and seals the entire area. Every electrical connection gets heat shrunk and sealed. It is not worth the money to buy "normal" heat shrink in my opinion. I can order the adhesive lined tube online for less than a tiny package of cheap stuff costs me at the auto parts store. Yes, regular heat shrink tubing works well and is tons better than electrical tape. I just want my connections to be waterproof and sealed from the elements so I never have to fix it later. The extra pennies per foot make it worth it in the long run. But either way, use heat shrink tubing.
Another great friend to the off-roader is dielectric grease. It is used in connections to keep water out. Use it on all connections that you do not solder or that have any chance of getting exposed to water. That for me means pretty much everything.
I always solder, its solid, simple and I never have to worry about it. I can also take it apart should I ever need to, you just re-heat it. Soldering is not that difficult, you just strip the wire and twist the ends together or insert it into your connector. Next you heat up the wire using either a soldering iron or torch and touch the solder to the wire. When the wire is hot enough the solder will wick into it, and when everything is nice and silver you are done. You do not need a huge glob of solder on there for it to be a good connection, just what wicks into the connection. Of course only use electrical solder and not plumbing solder. Never solder a dirty joint and make sure the wire is clean.
Here is a video covering the basics of soldering.

Next we will start to piece it all together
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