This is a Metra brand wire harness that fits most Volkswagen 1980-2007
 
This model number is 70-1784

You may use the fit guide at Metraonline.com to see which parts will fit your vehicle.

This harness is color coded and will help you install your new radio without having to cut off the factory harness. This is the right way to install a radio. You can solder this harness to your radio harness or you can choose to crimp it. 

Here are some tools and connectors that may help you install your own stereo:

https://www.franksaudiomotive.com/product-page/soldering-iron-kit-adjustable-temperature
https://www.franksaudiomotive.com/product-page/flush-cutters
https://www.franksaudiomotive.com/product-page/red-butt-connectors