The principle

21 pin standard interface

Here is the 21 pin standard interface as defined by NMRA (S-9.1.1 Electrical Interface & Wire Color Code E: 21 Pin Connector Interface), page 7 :

NMRA 21 pin standard interface

The 21 pin ESU interface

Here is the 21 pin interface as specified in the ESU document LokPilot_V40_Family_Users_manual­_Edition_3.pdf :

ESU 21 pin interface

A priori, no incompatibility. It was predictable, as it would be difficult to imagine a decoder manufacturer not complying with the NMRA. Therefore the decoder is not involved in the problem.

The LSM trick

If we look a little closer at the list of addresses to modify in the leaflet of LSM locos, we soon realize that the decoder outputs are redefined. Be aware that this list is different depending on whether the decoder is V3.0 or V4.0!

Output Assignment Comment
normal LS Models
Lights forward White front lights, red back lights Lighting of front cabin We understand why a cabin lights in place of the headlights with another decoder.
Lights backward White back lights, red front lights Lighting of rear cabin Same remark
AUX1, AUX2 At will Distress flashing Why does it need two outputs?
AUX3 At will Lights forward Conversely, how to control two independent elements (white lights and red lights) with only one decoder output?
AUX4 At will Lights backward Same remark

The trick is therefore to switch the auxiliary outputs, playing on the fact that the Lokpilot (and Loksound) have all their outputs direction sensitive, ie. they can be programmed differently according to the travel direction, which is not the case in other brands. I know of one exception: the Lenz Silver+ has an auxiliary output direction sensitive (in addition to the normal outputs for lights, of course).

This feature makes it possible to control the lights with an auxiliary output. However, there remains one enigma: only one output (eg AUX3) controls the white frontlights and the red rearlights. Then how are they made independent, since the red lights can be extinguished when the loco is harnessed to a train? To answer, the electronic card should be reverse-engineered, but this could damage it (double-sided circuit, tight components, etc.) I do not want to take the chance.