2002 Chevy Express 5.7 3500 dome/ box light

[Sparqee]

Hi all, my dilema is the dome & box lights wont work manually or with door switch. I have replaced headlamp combo sw because it needed it anyway, still no fix. Checked voltage at door jamb sw. 12v+/- present. Found what is either lighting control module or illumination control mod. under center dash on firewall, but cant find it in my Haynes repair manual, so my question (s) is , is this a possible cause or is there some advice as to direction to go from here? Thanks