I do not have a diagram for a 201 but there often is a method to the madness.

Red wires are typically constant power
Black wires are typically key switched power
Solid Brown wires are typically grounds, striped brown are the leads going to a switch that grounds the circuit to complete it (like your dome light)

The seat relay switch is on the hot side so it will be red wires
The dome light TK switches to ground so it will be brown wires

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech