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Battery Cables Wiring Harness
How to Build a Wiring Harness
This is my basic guide to making a wiring harness. This is one of those things that can be really frustraging, but if you take your time it will be much less painful. Every harness is different, so I'm going to show you the basics. The rest you will have to figure out - that's the fun part!
You will need the following:
Wire cutters - around $10
Wire strippers - $17
If your doing a lot it is nice to have a set of automatic strippers.
Crimping plier - $10
I like the GB GS-388, these do both insulated and non-insulated terminals.
You can also get fancier ratcheting crimpers that are $30-100.
Optional: multi-purpose tool - $10
These will strip and crimp. Not quite as nice as the 3 tools above, but will get the job done for less money.
Heat gun - $30-60
Multimeter - $20-100
This will help you diagnose electrical problems, and has about a million other uses.
Heat shrink - $0.5-1 / ft (depends on the size and were you get it)
Wire - price varies - various sizes, mostly 14-18 AWG (maybe some 10 or 8 AWG)
You can use most types of stranded wire.
I like GXL wire because it's more flexible than the standard stuff from the local electronics store.
Terminals - prices vary, various sizes and types
(you'll figure out what what you need as you go)
Zip ties - prices vary - get a bunch of sizes and lengths
Weatherpack connectors - price varies
I bought a 460 piece kit for $95 from DIYAutotune.com
You can use other connectors, but Weatherpack are very high quality and sealed, and if you buy a kit the price isn't bad.
You can also use Deutsch connectors. They're more expensive than Weatherpack, and a trickier to assemble, but they're more compact. Either will work fine.
Weatherpack crimp tool - $35 (there is another one that is $95, you don't need that, the cheap one is fine).
Before you cut your first wire, you'll need a wiringdiagram of your system. You can draw this with a pencil and paper if you want, but a computer program will make it a lot easier to draw and make changes. I use Adobe Illustrator (because I'm familiar with it). You can use lots of other drawing or CAD programs. Inkscape is similar to Illustrator, but its FREE. There is also a free circuit design program called XCircuit.
There will be two main parts of your wiring diagram. The schematic is a drawing of the circuit showing the parts and how they are connected. The other part that I find useful is a drawing of the actual wiring harness. Drawing the wiring harness separately helps you think about how you will actually connect everything, like the actual wires and connectors.
Below is the wiring diagram for my motorcycle.
If you study each part it should start to make sense. I divided it into schematics for the 12V system and Motor system (high voltage) on the left, and the wiring harness on the right.
Click the image for a PDF version.
In the Wiring Harness part, each of those pieces with colored circles stands for a pair of connectors. I've also color coded wires the same as they will be in the real wiring harness, and finally noted the wire gauges for different parts. To help me visually, I used thicker lines for the heavy gauge wires.
I made my harness so that things like handlebar switches could be disconnected by just unclipping a few connectors. This way you can take things apart without having to cut any wires, and you can do repairs to one part without affecting the other parts.
It really helps to keep everything organized. Try to keep wires from the same connector wrapped together. The more wires you have going all over the place, the harder it gets to diagnose problems if something goes wrong. I use a combination of heat shrink and zip ties to bundle wires together. Heat shrink can be taken off with a utility knife, but it's kind of a pain. Zip ties can just be cut with wire cutters.
Feel free to steal my wiring diagram and use whatever you need...that's why I put it up here!
Here I'm going to go through the basics. Every wiring harnes is different, so you'll have to do a lot of thinking and figuring things out (and messing up and doing things over again...that's pretty normal).
The first step is to strip the wire. Here's how an automatic wire stipper works. You put the wire through the right sized hole and squeeze the handle. The tool grabs the wire and then pulls the end off..
Once you have a set of these, it's pretty obvious how it works. I'm putting this up to convince you to stop torturing yourself with cheap wire strippers and just spend $17 for a set of these.
Attaching a Non-Insulated Crimp Terminal
We'll start here because crimp terminals are pretty basic, and also pretty cheap so you can practice and mess them up without worrying too much.
First strip the wire so that there is just enough to fit into the crimp area of the terminal.
Cut a piece of heat shrink that is a little bit longer than the stripped area.
Place the terminal into the crimper. The crimping pliers have places for insulated and non-insulated terminals, in two sizes each. Here were doing a non-insulated terminal (insulated is wrapped in plastic, see below.) The areas for non-insulated have a round side and a bumped side (the areas for insulated have two round sides).
The terminal has a seam on one side - this seam should go against the round part of the crimp area (on top in the picture below).
Insert the wire into the terminal, then squeeze down on the pliers. It might take a fair amount of force for thick terminals.
This is what the crimp should look like. The wire insulation got crimped as well - that's OK, it'll be covered by heat shrink.
I need to point out that in the picture below, the insulation is crimped but the wire inside is OK. You should not crimp so hard that you damage the wire, just enough to make a solid crimp.
Now turn on the heat gun and let it warm up. I set mine to 500 deg F. Slide the heat shrink over the crimp and heat it until it closes tight.
This heat gun has an attachment that redirects hot air back around the wire. Very handy for heat shrink work.
When done, it should look like this.
If the crimp is done right, you don't need to solder. You can if you really want to (I generally don't, and it is actually not recommended by the ABYC...see the FAQ)
Attaching an Insulated CrimpTerminal
This is very similar to the non-insulated, except you don't need heat shrink and you'll use a different crimper.
Strip the wire.
Place the terminal in a crimper. Here I'm using a multi-purpose tool (wire strippers and crimper). This is because the crimp pliers I used above are too wide and would crush the plastic end.
Insert the wire, squeeze down, and it should look like this.
Insulated terminals are nice because you don't need to use heat shrink, and the terminals are covered (althouth they're not water proof, they will keep water and dirt out for the most part). I personally think non-insulated terminals make a better connection because the crimp is better, and I just think they look neater.
Here's another thing you'll use a lot, a ring terminal. This one is 8 AWG and connects to the battery charger. I used adhesive heat shrink to seal the crimped area. I actually used a hex crimper on this one (see the Battery Cable page for more on hex crimpers). You can use a regular crimper on this, I just happen to have a hex crimpers.
Splicing Multiple Wires
There are many times you will want to splice 3 or more wires at one point. Here's how I do it (it's not the only way, but it works pretty well).
Below we have three wires that have been stripped about 3/8". At the bottom is a piece of crimp tubing. You can buy these at some electronic stores. If you can't find them, you can just get some thin walled aluminum tube and cut pieces about 1/4" long. At the top is a piece of heat shrink.
Insert the three wires into the tubing. The wires should go all the way to the end of the tube, maybe even hang over a bit.
Make sure you have the heat shrink on the wire before you make the crimp.
I make this crimp with the non-insulated terminal crimper. You could use the insulaed crimper as well - either will work.
This is what the crimp should look like.
Slide the heat shrink down and use the heat gun to shrink it.
Here I used adhesive heat shrink for a stronger bond (you can see the adhesive squeezed out of the ends.) You can use regular heat shrink, but adhesive will make a much better seal and mechanical connection for wire splices like this.
Building Weatherpack Connectors
OK, here's the cool part. These connectors will let you build a wiring harness that you can take apart easily. It will look just like a factory wiring harness (well, pretty close...)
Weatherpack connectors have a male and female side, each with 3 main parts. There are the housings, seals (small green rubber pieces), and terminals (metal pieces).
This is a close up of the Weatherpack crimper. With the standard connectors, you'll be using crimps 2-5.
First strip about 1/4-3/8" of insulation from the wire. Then slide a seal onto the wire.
Note that there are different size seals for different gauge wire. They are color coded. Green is for 20-18 AWG.
Place the terminal in the crimp tool as shown below. Make sure the jaws are only on the crimp area and not other parts of the terminal that you do not want to crush.
Insert the wire with the seal into the terminal while it is still in the crimper. Squeeze down and make the crimp.
The crimped terminal should look like this.
See the little metal strips around the seal? Those get crimped in slot 5 of the crimper. This isn't a very tight crimp, just enough to keep the rubber in place.
Now insert the terminal into the housing. Make sure you use the right housing. The male terminal housing is shown below.
Press the terminal in until it clicks. It helps to push against the seal so that it doesn't get pushed out of its crimp (which isn't very tight).
When you're done, close the flap that holds the terminals in.
Below I have a female connector with 4 colored wires. I've used a zip tie to hold the wires together.
Notice that the female connectors have a green seal around the outside.
Here are two connectors snapped together. All sealed up!
Don't worry if you screw up and need to take a connector apart. There is a little terminal extractor that makes this easy (one comes with the Weatherpack kit that I got). The extractor looks like a screwdriver with a hold down the center. You place the extractor around the terminal, push it into the housing and the terminal pops right out. (Sometimes you need to wiggle the extractor around until the terminal comes loose.) You can reuse the terminals again after they've been extracted.
Here is a picture of my wiring harness in the bike. Notice how I labeled the connectors - I use a silver metallic sharpie.
I know it looks like a bit of a mess, but that's how it is. There's a lot going on in a small space on a motorcycle.
The harness connects up to the handlebar switches, lights, and other things. Wires that go together are grouped with heat shrink. I then use a piece of split cable wrap to cover the wires and wrap it all in black athletic tape. (Yes, athletic tape.)
Electrical tape doesn't work that well, it dries up and falls off. Notice that I haven't used electrical tape anywhere in this whole harness. It's not bad stuff, just not as robust as heat shrink (and it looks kind of crappy, in my opinion.)
Those are the basics. The rest is practice, problem solving, and lots of patience. Just take your time and try not to get frustrated when you crimp on a terminal, realize you forgot the heat shrink...then realize you don't have any more terminals.
What are some ways I can save money?
Use a multi-purpose tool instead of separate cutter, stripper, and crimper. You can use a lighter, a small propane torch, or even a hair dryer instead of a heat gun. With a lighter or torch, be careful because it will melt right through the heat shrink pretty easily. A hair dryer will take longer (not as hot).
Another way to save money is to plan ahead. Every time you have to do something over, it costs twice as much. This is going to happen no matter how well you plan, but you can minimize it.
Buy in bulk. Most of these parts cost pennies to make, but get sold for several dollars. If you buy just one or two connectors or terminals at a time, they can end up costing twice as much (or more) as if you buy them in bulk packages. And shop around - since Radio Shack has basically become a cell phone dealer, their small parts are more expensive than they should be. Some of the same parts can be found at a different hardware or electronics store for a lot less.
Do I really need Weatherpack connectors?
Nope. You can use the cheaper plastic type (sometimes called a "Molex type connector"). They just aren't as nice for this application. They usually aren't sealed, and tend to break if you take them apart too many times. You can use large heat shrink to make a better seal, as in the picture below.
You can also reuse a lot of the connectors from your original wiring harness. Either leave them connected to the original parts (like handlebar switches), or cut the wires and splice them into your new harness.
When should I use regular heat shrink vs adhesive?
I almost always use regular because it's cheaper and it can be taken off with a utility knife. If I want something to be sealed, or just to make a stronger mechanical connection I'll use adhesive. It's good practice to use adhesive around wire splices (but keep in mind this will make it nearly impossible to take apart without cutting the wires).
I use twist-on wire connectors (wire nuts) in my house wiring? Can I use those?
No. They cut into the wires and are likely to come apart with all the vibration in a vehicle.
Why don't you use solder?
Mostly because it's not necessary. Good crimps will hold up well. Adhesive heat shrink will help if you want to go the extra mile.
It is also possible solder can be worse when there is a lot of vibration, at least according to the ABYC wiring standards (American Boat and Yacht Council). According to them:
Another common misconception dictates that the best of all connections is a soldered connection. However with stranded wire, the solder bonds the individual strands together, making a solid, inflexible wire. ABYC standards prohibit soldering as the solemeans of making a connection because the newly solid wire is subject to cracking or breaking through vibration and flexing. A more practical solution is to use a crimp connector described above. Wires should never be joined simply by soldering and taping (or heat shrink); however, if solder is used, use only 60%/40% rosin core or solid solder, soldering after the butt connector is crimped. Acid core solder as used in plumbing may never be used in any electrical wiring.
So if you really want to, crimp and then solder. It will probably be bombproof. But don't just solder.