Soldering wires & connectors

Part 1. Preparation and safety

Objective

• Correctly solder an electrical connection to an electrical wire.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• The soldering iron tip needs to be very hot in order to melt solder. Do not burn yourself with the soldering tip.
• Do not inhale the fumes that are released during the soldering process; they can irritate your respiratory system.
• If the soldering iron is electrically heated, do not use it while standing in water or engine coolant.
• Never apply solder to a live electrical circuit.
• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Solder used in automotive electrical applications is an alloy typically made up of 60% tin and 40% lead. Solder needs to change from a solid state into liquid easily and return to its solid state quickly.
• Solder is available as solid or flux cored. Solid solder requires an external flux to be applied in the soldering process. Flux cored solder has a bead of flux through the center of the solder. Flux cored solder is also referred to as rosin cored solder
• Flux is needed to prevent the metals being joined from oxidizing when they are heated. Flux is normally acidic and needs to be removed after the soldering process so that the join does not corrode.
• Solder is applied with a hot soldering iron. The soldering iron is heated electrically or by an external source such as a butane or oxyacetylene torch.
• The soldering iron tip absorbs heat that is then applied to the materials to be joined. Once they are hot enough, solder is able to melt between the components.
• For a connection to be successful, the soldering iron needs to be "tinned". The tinning process assists in transferring heat to the wire. The soldering iron tip is heated, and a small amount of solder is applied to the tip. Excess solder is removed with a cloth rag.
• The soldering iron tip is applied to the wire so heat is transferred to the wire. Do not apply too much heat or the insulation may melt.

Part 2: Step-by-step instruction

1. Safely position soldering iron
   When using a soldering iron you must be careful not to burn yourself or any part of the vehicle you are working on. The tip of the soldering iron has to be hot enough to melt metal solder, so make sure it is in a safe position and not touching anything.
2. Prepare the wires to be joined
   While the soldering iron is heating, remove an appropriate amount of the protective insulation from the wires. Always use a proper stripping tool that is in good condition. If you intend to seal the join with a heat shrink sleeve, cut a section of this tubular material long enough to overlap the cable insulation on both sides of the join and slide it over the end of one of the wires before joining them.
3. Join the wires mechanically
   Twist the wires together to make a good mechanical connection between them. If there are impurities in the solder, and the wires are not directly touching each other, then although there may be a strong physical connection there may not be a good electrical connection. This is known as a ‘dry joint'. It is also very important that the surfaces be very clean before soldering or there will be a poor connection.
4. Apply solder to splice
   Use the soldering iron to gently heat up the wires and melt some solder. Place the soldering iron onto the joined wires to ensure that just enough solder runs smoothly into the wires. Be careful not to use too much solder and if you apply too much heat, you will melt the wire insulation. When you have finished soldering, clean any excess flux from the joint with a rag and a little solvent.
5. Sleeve the join
   Once the electrical connection has been made, and it has cooled down enough for you to be able to handle it, slide the insulator sleeve cover over the join. There are different types of sleeving. The most popular type is shrink wrapped onto the join with a heat source. Another type contains a glue which when heated melts into and seals the joint. If there is no heat shrink sleeving available, then it is possible to seal and protect the splice with electrical insulating tape.
6. Check the connection length
   To solder a wire to a terminal connector, you will get a better connection if you do not twist the wire strands together tightly before placing them through the terminal as this gives the terminal more surface area to come in contact with the wire when soldered. However, it can be difficult to insert the wires in the terminal if they are just loose strands, so twist them just enough to help you insert them cleanly. Place the bullet or terminal onto the wire to check that the stripped part of the wire does not extend beyond the insulated shoulder of the terminal. Then remove the wire from the terminal.
7. Apply solder
   Give the wires a thin preparatory coating of solder. This is called ‘tinning’ the wires and helps to make the final connection. By using rosin or resin cored solder, it is unnecessary to prepare the surfaces with a flux material as this is incorporated into the core of the solder. Put the wire back in the terminal, and place the iron onto the terminal to get it hot enough to melt some more solder between the terminal and the tinned wire. Be careful not to use too much solder, and if you get the terminal too hot the wire insulation will start to melt.
8. Cover the terminal
   Once the electrical connection has been made, and it has cooled down enough for you to be able to handle it, you can then place the insulator cover over the terminal and place the connection into service.