Here are some observations regarding Märklin insider locomotive and passenger wagon set 39781, 43141. I don’t have a permanent layout so I have just tested on a test track.


First of all, I’m quite happy about this set, locomotive and passenger wagon set is well-matched, and looks quite nice. I do like that the interior lighting is controllable from the locomotive decoder. I wish more models had that option. In my opinion, the interior lighting is a bit cold white.




The decoder is using a relay to supply current from the track. The initial wagon current draw is quite high. I measured a short peak at just above 4 A. So, it seems that there is installed some capacitors in the wagons. The continuous draw is around 0,025 A. (measured the whole wagon set.) I discovered this when I tested the passenger wagon set on another locomotive where the decoder feeding the current without a relay. Luckily the decoder protection worked. Wagon lights flickered some seconds before they came on. So, a warning: you may damage the decoder, if you use 43141 on locomotive where the power comes from a decoder without a relay.



The locomotive sound is what I would classify as standard Märklin sound quality, it's ok for my use. The smoke generator is a standard one and works ok. According to a thread on Stummis forum, the smoke generator is also on a relay. https://www.stummiforum.de/viewtopic.php?f=2&t=173995&hilit=39781
The tender coupler seems to be adjustable, but for me, it would not click properly in place in the inner position. In the normal position, it clicked nicely into place and the position holding was acceptable.
Normal position:


Coupler close up in normal position:


This picture shows almost in inner position but not quite, it slipped a bit out before the picture was taken.



Summary:
Good quality models, and many details.
Locomotive feels good and heavy, heavy tender.
The current-conducting coupler on the tender can be controlled digitally.
Nice yellow headlight.
Built-in smoke generator. (I think I addicted to locomotive smoke)
A lot of sound functions, decent sound quality.
The cab lighting is a bit to cool white.
passenger wagon set matches the locomotive vell
the wagons have built-in led, but a bit too cold white (in my opinion)
the figures are nice spaced around.
the car’s complement the locomotive nicely.

Have someone else tested the inner position and has experience?
Have someone opened the passenger car and could confirm the capacitors?