Would anyone have a detailed wiring diagram for the Marklin 37844? Many thanks!!

Many thanks Jean! In fact my locomotive was dropped and the blue wire coming out from the tender popped off, and so did the brown wire. Both are still attached to the tender. The precise problem I have at this point is that I don't know where to re-solder the blue wire. I know that it has to be soldered to the motor, but I can't figure out exactly where to. Again thank you for you helpful message. Kind regards

For the green and blue motor wires, they go to the motor shield. Take notice of where the green wire goes, and the blue should be on the other side of the shield on the same type of pad.
e.g. like this: (they can be swapped)

the brown wire goes to the chassies ground, e.g on a soldering pad on one of the two motor shield screws. In the picture its hard to see, but its on the screw below the blue wire.

Note that, according to the märklin exploded drawing, your locomotive has a permanent magnet (same as in the picture above), part no 389000 or the same as included in 60941, so a 60906 decoder is not suitable.

and if you need more information on the decoder. According to the Märklin Part list, the decoder part number for your locomotive is 602758 so try googling that number, it should give you some pictures you can use, but look at the pictures and make sure it's the same decoder. Also check the number printed/embedded on the decoder in your locomotive.

ref 37884 Exploded drawing: https://static.maerklin.de/damcontent/ac/20/ac20aee0a3e03e2dcac00f5f36ab2b391434542118.pdf

Merci beaucoup Jean !