Apparently the body control computer decides (incorrectly) that the current to the taillights is over-spec. So in response it turns the tail lights off completely. It would be interesting to know the reason why the body control computer makes that mistake? Computer fault? Broken solder joint? Wrong part installed?
I can see why Ford engineers might want to add a safety function to have the body computer check for short circuits developing , b/c a short circuit could cause a car fire. But if that causes the taillights to turn off when there’s no short circuit, seems worse than not having the short circuit detecting safety function. Another example of the complexity vs reliability compromise maybe?
Visit NHTSA.gov and check the recall for the Mavericks. They might tell you why. I’d guess that level of detail might not be posted for a while if at all. Still, they coordinate recalls and could have your answer.