Check the pig tail that plugs into the alternator. Those wires are known to break or pull out. Perhaps when you hit a bump it jars it loose just enough but goes back to making a contact.
'14 Tuxedo Black ST3
'13 Ingot Silver Escape Titanium AWD
'04 CD Silver SVT, #877, 1 of 135 May 2011 ROTM, FF11: Best Display, Best of Show; AFN12: Best SVT, Best Audio, Finest Five, Carlisle Nifty Fifty