Righto....maybe instead of tracing the wire from the switch that goes into the nest behind the dash, try looking on the undercarriage or in the usual places for a wire(s) where a light or set of lights may have been mounted, likely in a bundle and zip tied. Any evidence of brackets or mounts from lights or a light bar? I have both fogs and driving lights, light bar, rock lights and roof rack pod lights.....
'03 Ford E350 7.3L Diesel
(de)SMB'd Custom RB-50
Quigley 4X4 w/Deavers & Agile Offroad's R.I.P. package
CCV High Profile Pop Top