Here are a few sites that should explain exactly what you need. They really helped me when I was building my rack.

http://www.beanfarm.com/heating/Flexwatt_Wiring.pdf

http://www.arbreptiles.com/cages/flexwire.shtml

and last but certainly not least...

http://www.slitherinsisters.com/how-...e-flexwatt.php

Hope that helps!