Hi Tom,
Not familiar with Airwire only the P8. If you do not have the wiring diagram for your Forney this link will take you there.
http://www.bachmanntrains.com/home-usa/dwg/dwgs/LS_Baldwin_2-4-4_Forney.connection_diagram.pdfStart by checking the connections from the chuff sensors to the P8. Check the Phoenix site to see if they have specific instructions for the Forney related to connecting the chuff sensor to the P8.
The guys at Phoenix are incredibly helpful so you may want to call them for help. They are vary helpful with great knowledge on specific problems.
I have no suggestions on how the Airwire controls the lights so can't help there except to say after a good rest go back and start over completely following the instructions for the lighting circuits making sure they are correct. In many cases a simple reversing of the wires to the headlight will do the trick since the LED's are polarity sensitive.
That is all I can offer, hopefully others will have better ideas.
Good Luck.
Bill