The 1990 Cadillac DeVille doesn't have a readily accessible, manually operated fuel shutoff switch like some older vehicles. The fuel system is controlled electronically. In the event of a crash, an inertia switch will cut the fuel supply. This switch is usually located under the dash, sometimes under the carpet on the passenger side. It's often a small, easily overlooked button or lever.
To find it: you'll likely need to consult your owner's manual or a repair manual specific to that year and model. Online resources might also have diagrams showing the location.
Keep in mind that attempting to disable the fuel system yourself might be difficult and could damage other components. If you have fuel system concerns, it's best to consult a qualified mechanic.
