I had a decoder fitted in my control car a few years ago at which time the car was assigned its own address on the Massoth. When the car is used on a train that address is activated ensuring that it is running the same direction as the rest of the train will be running.
I then activate the address of the loco to be used and off we go.
I think that interior lights in the control car may be controlled by the same decoder (which I think is a Massoth) but I would have to check as I've not run the train for some time. It is possible that interior lights are controlled by the switch under the car rather than the decoder. Give me a couple of days and I'll give the train a spin to see how things work . It will give me an excuse to get the train out!!
In the meantime here's a pic of the train running a few years ago. Headlights are on but interior lights don't look as though they are on:
