I had a spare Dapol imperium that wouldn't operate the cab lights and I think it is the same decoder rebadged, in the end I bought a esu lokpilot 5 that worked fine.
It only needs 5 functions front/rear marker lights, front/rear cab light and carriage lighting.
The problem with the Bachmann decoder is the logic levels are wrong on the function output for the carriage lighting.
Mine also has a lenz silver 21 pin decoder, the packaging and instructions of the bubble car are ambiguous saying mtc21 because true mtc decoders with logic level outputs on aux 5 won't turn the carriage lights off.