You didn't specify whether or not you were looking for info on a car or truck, but here is the info for a 1940 Ford Truck serial location: 4 cylinder - on top of frame left side, ahead of dash. also on left side of flywheel housing 6 cylinder - on left frame member ahead of cowl. also on top clutch housing 8 cylinder - on top of frame, left side near dash. also on top of clutch housing

Serial numbers are located on the left frame side member near firewall.