Any ideas? Just unpacked my On30 Heisler and it only runs in reverse! When I reverse direction there is only 4 volts measured across the track. When I remove the engine there is 17.5 volts.
This smells like a short circuit to me.
you could measure the current that is flowing when measuring 4 and 17.5 Volts.
If the current is high when measuring 4 V there is a near short somewhere.
Ton