The Lineman's Splice: How to Make Reliable Electrical Connections in Your Vehicle's Wiring Harness
Soldering Splices
Brightfour Low Voltage Wire splice connectors - Pack of 12 Quick Solderless T Tap Connector 1 Pin,Rock Solid Connector for 24-20 AWG Cable for Vehicle/audio/video/Lighting and Automotive Uses - Amazon.com
Splicing Into Wires | Evilution
Soldering Wire Splices. Wires should be at 90 deg. Twist wires equally to form a neat splice. Solder connection. Pigtail Splice. - ppt download