1992 Mighty Max starting issue

1992 MM V-6 4x4 engine won't turn over unless the unlock swith on the dash is depressed....I suspect a problem in the clutch linkage....possibly a switch...neither the haynes nor the chiltons manuals cover this area...any help would be appreciated......also, truck is running rough...it lags and hesitates when given gas and will try to cut off...there is a low grade back fire at times....tends to smooth out after engine warms up.