The vehicle speed reading is diguested by the traction control system (ESP) and transmitted via CAN to the instrument cluster, the engine, the transmission, and who knows who else. Anyone wanting it will have to engage the CAN and speak the right language.

In other words there is no speed signal wire to the instrument cluster.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician