When you replaced the Wiper motor - was it "exactly" the same Ford number or the Motorcraft equivalent?
This sounds like the wiring harness - the plug that goes into that motor may need to be rewired.
The connector should have 4-wires on it. One goes to ground - the other three go to the Body control Module.

So if your system is telling you PARK is short to "live" then you have a bad ground wire return at the Wiper motor - Pin 4 looks to be the cause of the error - possibly broken or corroded off it's ground point. You can always make a new one to fix that problem.