Check Glow Plugs
WARNING: This page is about a different car, the 1995 Ford RV Cutaway, 1995 Ford Econoline, 1995 Ford Cutaway, and 1995 Ford Club Wagon. However, it is still accessible from the selected car via links, so may be relevant.
With ignition off, disconnect glow plug connectors at glow plugs. Connect a 12-volt test light between a convenient power source and each glow plug terminal. If test light illuminates, go to next test. If test light does not illuminate, replace glow plug and go to next test.