Proper soldering technique.
NCG wanted a quick guide on how to do this, and it's too long for a visitor message. So here you go!
EDIT: Anyone who says to use crimp connectors can eat my ass with a spoon.
You'll need solderhttp://i839.photobucket.com/albums/z...e/PC280357.jpg (cheap), wire strippershttp://i839.photobucket.com/albums/z...e/PC280356.jpg (fairly cheap), the proper size heat shrink tubing for your gauge wirehttp://i839.photobucket.com/albums/z...e/PC280358.jpg (cheap), a lighter to heat up the shrink tubing (cheap), and the solder gunhttp://i839.photobucket.com/albums/z...e/PC280355.jpg. (Sorta pricey, so try to see if you can borrow one.) You might also need a small file, but it's not necessary if you're careful.
Optional items are fluxhttp://i839.photobucket.com/albums/z...e/PC280359.jpg and electrical tapehttp://i839.photobucket.com/albums/z...e/PC280360.jpg. Flux helps the solder flow and melt and you know what electrical tape does. These are optional as the heat shrink replaces the electrical tape and the solder I'm recommending has the flux made into it.
Make sure the solder is for wiring and not for copper piping. Go to a RadioShack or the equivalent and purchase the 60/40 blend rosin core solder. DON'T get the 40/60 blend. It's crap, and wont' flow properly, and is just basically awful.
You'll start one wire at a time. Locate the proper wire coming from your car that attaches to the same wire in your new harness. We'll pretend these yellow wires are in your car. One end is attached to the new harness, and the other is in your car. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280361.jpg Take the wire strippers, and strip the ends of each wire. 2 Pics. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280362.jpg http://i839.photobucket.com/albums/z...e/PC280364.jpg You'll note that the wire strippers have different size holes in the jaws for different gauge wires. Make sure you're only removing the rubber insulation around the wire and leaving the wiring inside.
Now cut a piece of heat shrink and slide it over one of the wires. Move it at least a few inches away from the end of the wire because soldering is hot, and the heat shrink will shrink before you want it to. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280365.jpg
You'll notice the exposed wires are actually many tiny wires wound together. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280364.jpg Unwind them and fan them out. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280366.jpg Now take both wires with the fanned out ends and weave those ends together. 2 Pics. (SPOILER)
http://i839.photobucket.com/albums/z...e/PC280367.jpg
http://i839.photobucket.com/albums/z...e/PC280368.jpg
Take the soldering gun and heat up the wires at the new joint you've made. (SPOILER) http://i839.photobucket.com/albums/z...e/PC280369.jpg Once it's hot enough, with the gun still there, begin applying solder. It should melt and flow into the wiring. Once it's thoroughly soldered remove the gun and give it about 20 seconds or so to cool down.
Check the joint for any sharp edges. File those off and make sure the joint is nice and smooth. (If you're careful how you weave the wires together, you can avoid those sharp protrusions.)
The finished joint.http://i839.photobucket.com/albums/z...e/PC280372.jpg
Now you're ready to slide the piece of heat shrink over the new joint. Heat it with a lighter until it shrinks and seals around the new joint. (SPOILER)http://i839.photobucket.com/albums/z...e/PC280374.jpg
Heat shrink is superior to electrical tape in this application as it seals more tightly around the joint. They both keep out moisture, protect the wiring from shorting out, and give the soldered joint reinforcement.
The finished product.http://i839.photobucket.com/albums/z...e/PC280376.jpg
Make sure the new joint is fully covered by the heat shrink and move onto the next wire.
