Soldering 101

This is a general introduction to soldering electrical connections on your bike. This example is for connecting a ground wire to an extra brake light socket, but the method is the same for any soldering that needs to be done.

A few things to remember before you start:

• Get a ~30 watt pencil soldering iron. They are available at Radio Shack, Circuit City, or, in Canada, The Source, for about $10. Try to pick up a soldering sponge or two at the same time.

• Make sure you tin your tip before using it. That means: soak it in solder, knock the excess off, and wipe it clean with a wet soldering sponge. If you don't have a soldering sponge, a damp cotton or terrycloth rag do the trick. This will not only extend the life of your tip, but by having a clean tip, you will produce better joints, more quickly, and with less heat damage to surrounding components.

• You want to be using rosin-core electronics solder, about 16-22 awg, not that big thick stuff designed for plumbing. You want either a 63/37 or 60/40 tin/lead alloy. The 97/3 and the "lead free" stuff are both inferior. They make it harder to visually inspect the joint, because they have a naturally duller appearance; also, they require higher temperatures, which means that your iron or your wire's insulation may not be up to the task.

• Flux is superfluous when soldering electronics (not copper pipe), as flux is included inside proper electronics solder ("rosin-core").

• Always apply heat to the object being soldered, then apply solder to the object, not the iron, no matter how tempting it is. Solder flows toward heat (ie, the iron), so put the iron at the end-point of where you want solder to go.

• A good solder joint will be shiny silver, not dull. You should be able to tug lightly on the joint (don't yank on it, just gently pull), and it shouldn't come apart.

• In general, you want to start with a good mechanical connection (ie, wires twisted solidly together) before soldering, then use solder to "glue" the joint together. This isn't always possible, but it's a good goal. Laying one wire on top of another and soldering them together will make a joint which is more likely to fail than one in which the things being soldered are already solidly connected.

Directions

Explanation: "Tin the X" means to cover X in a super-thin layer of solder. One effective way to solder two pieces together is to tin each piece, touch them together, and apply heat to the larger one until the smaller one's solder melts and the pools join together. This will create a good electrical and mechanical joint.

Steps 1 and 2 are to tin the bulb socket and wire; the sub-steps describe how to achieve this with each piece.

Step One: Tin the wire you are about to solder

1a. Heat the wire with the soldering iron
1b. Touch the solder to the wire so that the (stranded) wire "wicks" it in. Don't leave the iron on so long that the insulation melts.
1c. Use as little solder as possible

Step Two: Tin the socket

2a. Sand a spot on the socket so that bare metal is showing
2b. Heat that area of the socket with the iron. Hold the iron at a 45 degree angle to the socket so that the tip of your iron makes maximal contact
2c. Touch the solder to the socket until it melts and pools
2d. Use as little solder as possible

Step Three: Make the connection

3a. Hold the iron as above, but also touch the tinned portion of the wire to the socket
3b. When the solder which was on both the socket and the wire has melted, remove the iron. Do NOT move the wire until things have cooled down again
3c. Your goal is for a nice, shiny connection
3d. Note that in this stage you are NOT adding solder

Next, it is advisable to protect the joint from the elements, but this is not really necessary. 3M rubber electrical tape works well here. It's like regular electrical tape, except it's made of rubber rather than vinyl, and is quite a lot thicker. Hot glue also works for this.

You can consult this page for more information: http://www.epemag.com/solderfaq/default.htm
Look for the Soldering Photo Gallery at the top of the article.

There is also another article called Soldering 101, with more photographs.