Actually the homelink only uses the same 12V and ground that the autodim uses. The other wires are for side dimming mirrors (they use the sensor in the rear view mirror), reverse lock-out, or other convenience features such as disabling autodim unless the headlights are on, disabling autodim if the dome light is on...etc.

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Daily Driver: 02 E430 4MATIC
In the family: '03 E500 // '04 ML500 // 64 220SE