BadPennyKenny-
I assume it has failed. If it hasn't, you should be able to find it by activating the emergency flashers, and find it by ear.
Ford changed the E-series slowly, so you may find the flasher under the dash, near the steering column, which is where it was on my 1996.
If you are going to keep this coach for a while, you may want to get a copy of the wiring diagram book (links
here,
here,
here and
here). On eBay there are also entire sets of manuals for the 2008 Econoline (link
here).