How to check if the seat mat is 3-wired in Mercedes A W176, B W246, C W204, ML W166 and some others?

The seat occupancy sensor in most new Mercedes models may have 2, 3 or 4 wires:

  • white, red, brown (3-wired mat)
  • blue, brown, black (3-wired mat)
  • black, black (2-wired mat)
  • white, red, brown, green (4-wired mat in some models with WSS system, although wires colors may be different in case of the 4-wired seat mat)
Below there are photos of the versions. The photos were taken under passenger side seat.

3-wired seat occupancy sensor
- brown, blue, black:

3-wired seat occupancy sensor
- red, white, brown:

2-wired seat occupancy sensor - black, black:

4-wired seat occupancy sensor - GLA USA

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