man this was a common problem with many Fords about 20 years ago, I thought that they got this corrected a long time ago. Back then it was a relay or module that would stop working when it got too hot from engine heat that was given off. I doubt it's the same part, but the symptoms sound very similar. Sorry I couldn't be of any help, but it sounds serious enough to have a dealer/technician diagnose it, likely something that is common to the vehicle that they have seen before. | 
