When I print to pdf the pdf is always light what do I need to do to setup it to print dark?

Try Export Vector PDF:

1. Go to menu: File | Export | Postscript PDF... 

2. Verify Format Type is "PDF"

3. Press button Next, and proceed with PDF Layer selection.

Note:  It is here that you can select whether you want to have certain layers as Dark or Clear.

Here's a quick tutorial movie where I export a plane layer as negative (in the PDF), let me know if that helps:

https://numericalsoftware-update.s3.amazonaws.com/tutorials/2016-07-07_13-01-55-pdf-vector-export-negative.mp4