Wires are strips of metal often covered by an insulator. They are meant to direct the flow of electricity from one component to another. The ends of wires may be directly attached to components or use connectors to make some sort of attachment.
Solid Wire
Solid wire only has one piece per cable, and thicker solid wire can hold a bend. Some wires are so small that they can only be produced as a solid wire. Most solid wires used in vehicles are small.
Stranded Wire
Stranded wire has multiple pieces in it, which makes it easier to work with and allows chemicals (such as solder, used to hold wire to other components) to seep in to the ends. Some wires are so thick that they must be made stranded, or else they would be rigid or would bend with too much difficulty. Because of their flexibility, stranded wire the most common type found under the hood and throughout the vehicle.
Conductive Material
The most common conductive material used in wires is copper. Sometimes aluminum is used, and there are a few other types of metal that are sometimes used for special applications.
Wire Protection
Damaged wires can break circuits, short out to ground, or even short out to another circuit. Proper wire protection can prevent this issue from occuring.
Wire Insulation
Insulation is applied to wires so that they don't short out any time they touch another metal object. The insulation can be found in many different colors, including colors with a stripe of another color on them. The colors are often used to indicate different components and polarities, such as red for positive and black for negative on battery cables. Sometimes wires heading to a left component and right component will have the same color with a different color stripe. The color and stripe combination also makes wiring diagrams helpful, since the diagram can tell you what a wire goes to just from looking at it, instead of having to follow every wire in a bundle until you have found the one that leads to the proper component for the work you are doing.
Heat Shrink Insulation
Heat shrink tubing is a layer of insulation that can be added to individual or multiple wires to provide a stronger seal against the elements. They typically need to be applied to the wire before permanent attachments are made to both ends, because the material may not fit over the attachments. The material is put in place and then heat is applied to shink it down over the wire, and sometimes components as well. The material has only so much shrink potential, so the correct size must be selected for good results.
Shrink Ratio
Heat shrink is available in varying shrink ratios and quality levels. The popular motorsport grade Raychem DR25 is most commonly available with the shrink ratio of 2:1.
Dual-Wall Heat Shrink
Dual-wall heat shrink tubing has an outer layer that looks like normal heat shrink and an inner layer of some form of adhesive. This is often used at wire loom branch points or other special situations. It is often applied over standard heat shrink that has had its surface scuffed up to improve the bond of the adhesive.
Wire Connectors
Wire connectors are typically found at the ends of wires to give them some sort of connection, such as a terminal or ring. Terminals are a common male or female connection. Ring terminals allow for a bolts or screws to hold down the connection, as long as they are conductive (nylon or plastic screws won't work in this situation) and make contact with where the electricity needs to go. More substantial connectors are used at points where disconnecting has been deemed useful for service, such as right where a wire meets a component, or where a harness can be disconnected for the service of an assembly, such as during an engine removal.
OEM Style Connectors
Original equipment manufacturers source a wide variety of connectors to not only meet wire count needs, but also to help prevent situations where the wrong component gets plugged in to a given set of wires. If you want an online community or parts retailer to help you identify the type of connector you need, note the following:
- Is it a plug or receptacle?
- What is the approximate shape it forms when looking straight into it?
- What color is it? (Note if it's lighter or darker than other connectors of similar color on the vehicle.)
- What is the pin count? (Note: Wire count is misleading when two wires go into a three pin connector!)
- What keyways does the connector have?
- Where on the vehicle did the connector come from?
Connector Cycle Rating
A connector's cycle rating (or mating cycle rating) is the specified number of times a connection point can be disconnected and reconnected while maintaining its electrical connectivity. This is almost never made clear on the connector itself, and is sometimes a surprisingly low number of connections, such as merely three. It is often very difficult for a home DIY mechanic to find this information.
Current & Wire Guage Ratings
Different connectors are rated for different levels of amperage and wire guage. You should always check the product you're working with for exceptions, but the general specifications are depicted in the following table:
| Connector Rating | Current Per Pin | Thinnest Wire Guage |
|---|---|---|
| DTM/DT Mini | 7.5A | 18 AWG |
| DT | 12A | 16 AWG |
| DTP/DT Power | 25A | 12 AWG |
Soldering
Soldering is often the preferred method for attaching two pieces of stranded wire. It involved melting a metal solder with a relatively low melting point, then letting it cool down so that it hardens, providing a solid connection both physically and electrically. The following video provides some examples, and including showing some examples of flaws.
Shown here are a few examples of solder attempts, with comments about how some could have been done better.
Why Cars Use Stranded Wire Instead of Solid by Cars Simplified
A wiring harness is a full assembly of wire that is weaved through a vehicle to connect to all or nearly all of the electronic components.