Well, it could go bad. You need to check continuity, and check for voltage at the switch.
I tripped the inertia switch on my Lincoln Mark VII (virtually the same vehicle mechanically as 86-93 Mustang) when I repaired my rear cowl. The repair involved a whole lot of hammering right over the switch. When I was done, no start. Hotwired the fuel pump relay, started right up. Checked the inertia switch, sure enough it was tripped.
At Menards a guy had the trunk of his Gran Marquis stuffed to the gills with stuff like plywood and 2x4s. When I came out he was spraying starting fluid into the air cleaner and it was firing. I walked over, pushed the switch, it started right up.
"Sugartastic E Shizzle"