If you are not the original owner of your van, you might want to get in there and look under the dash to see what kind of wiring might have been done by the PO. This way you can get a sense of what types of wires and supplies you will be needing. I should have dissected my setup before installing the AMP, but since the radio worked fine I thought that wasn't nescssary. Wrong!
Here's a link to a site I find has helpful suggestions for audio DIYers www.CarAudioForum.com.

-Tracey