Major League Baseball has launched an investigation to determine why and for what purpose Diamondbacks coach Ariel Prieto was wearing an electronic watch during their wild card game Wednesday night against the Rockies, The Post has learned. In a picture obtained by The Post that MLB has seen, Prieto is shown wearing what appears to be an electronic watch three weeks after Commissioner Rob Manfred sanctioned the Red Sox for having personnel wearing such a watch in games against the Yankees. Prieto, a former major league pitcher, has been a coach/interpreter for the Diamondbacks the past three years. Arizona defeated Colorado 11-8 in the wild card game to advance to the Division Series against the Dodgers. The Red Sox were fined an undisclosed amount for their use of an electronic watch during August games against the Yankees. That was generally not considered a significant sanction, but at the same time Manfred issued a statement re-asserting the rules against electronic equipment in the dugout and declaring: “All 30 clubs have been notified that future violations of this type will be subject to more serious sanctions, including the possible loss of draft picks.”