The SIT uses a small HO motor to operate the piston for the smoke unit. The tender picks up track power and routes it to the locomotive via two wires and also powers the SIT via a switch under the tender. The e-unit in the locomotive is similar to Lionel's, but uses two-two finger contacts, a drum and plate/pawl assembly. The drum usually needs to be cleaned and the pressure of the fingers on the drum is critical to make good contact. I usually remove both sets of fingers and the drum, clean all three and reassemble. Brushes typically stick in the brush holder, so remove the brushplate, clean, replace brushes and reassemble.