Combine wafers, pecans, powdered sugar, salt and 1/4 cup cocoa in food processor. Pulse until wafers and nuts are crumbs - it's OK if there are a few pieces the size of small corn kernels. Add rum and dark corn syrup and pulse until combined.
Sift remaining cocoa in a large bowl. Form 1-inch balls by hand and drop in bowl with cocoa. Roll around in cocoa to cover. Store in covered tin.