Checked under the carpet on passenger side. Can only locate the cruise control amplifier, SRS voltage converter, anti-theft alarm control and X11/13 which is the SRS test connection.
No box with a button.
I disconnected the battery again but no luck.
The red LED does go on (X11/4) every time I turn the key to the #2 position. If I press the button for 2 seconds it will go out, but will light up again when the key is turned to #2 position.

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1993 190e 2.3
Spruce Green Metallic
62k original