Your problem is the light switch. If you listen close, you will hear a click from the light stitch when it happens. Ther was a recall on them about 2-3 years ago for this. Ask your Ford dealer if yours is covered. If not, get the switch from one of the regular parts store for about $60, It will be around $100 from For5d, if they do not cover it on the recall.
-----1993 Bird 5.0------
393 stroker, Vortech YSi, on E85
Lentech Strip Terminator & 4,000+ RPM stall converter
Detroit Locker with 3.55 gears.
17x9 Cobra Rs with 255/45/17 BFG KWDS
275/50/17 M&H DR on the rear