Does anyone know how to wire
D4120 duct smoke detector to the furnace (Goodman)

Is this for a dwelling or something more commercial?

This took me exactly 3 seconds to find: http://www.greenheck.com/media/pdf/manuals/smokedetectorD4120install_iom.pdf

If you need more than this you should not be doing this install!

Ah...Stan, I was headed in another direction...
If you're not sure how to install this, you likely have not
taken out a permit or are qualified as a fire alarm installer or
electrical contractor. If so, doing this in a location where the public
may have access puts the premises owner and unqualified installer in
a legally questionable position...
This was my curiosity...