Rickford is not a German spelling; it was probably Anglicized from something German. Are you sure John was born in "Pommen, Rheinland-Pfalz"? GOV, the historical gazetteer shows no such place:
http://gov.genealogy.net/search
Perhaps he was born in Pommern (Pomerania). It's a lot closer to Brandenburg than the Rheinland is, and would make a lot more sense.