At the 1977 European Junior Championships in Donetsk, Wagenknecht won gold in the 4 × 400 m relay (as part of the East German team) and silver in the individual 800 m (behind his teammate Andreas Busse). In 1978 Wagenknecht became East German champion for the first time, running a personal best 1:45.84 at the national championships to defeat Jürgen Straub and Olaf Beyer; at the European Championships in Prague later that summer he was eliminated in the semi-finals as Beyer won gold.