Jeff, these are my engines of choice.
What Joe says is right. These engines are more suited for a transformer like the Lionel 1033 using the B-U settings of 0-11 volts. Or a modern transformer that starts with lower than 6 volts to the track.
The 6-volt starting minimum to the track of the ZW will cause jack-rabbit starts and stops, without rewiring the motors to a series arrangement versus the parallel wiring as they come with. When people complain about the jack-rabbit starts and stops of these locos, I realize they're using a typical postwar transformer with that 6 volt start to the track.
Some of the later K-Line locos of this type came with a switch beneath the engine for either series or parallel running to accommodate postwar transformers.
I generally use 6 volt bulbs in my locos, as I use a 1033 with the B-U setting, which allows the locos to run just fine without burning out the light bulbs. For others, I go with a 12 volt bulb.
You must have gotten this engine for a good deal right? Because generally you run higher end engines, at least as I've seen you post.