David, depending upon the build date of your 300E, the control in the instrument panel is not the dash light illumination control.
Mercedes realysised that there were too many lights for the small rheostat to handle the electrical load.
The fix is a solid state voltage controller located behind the instrument panel attached to the body.
The control you turn changes the input voltage to the S/S controller which then supplies the needed voltage to the lights.
All lights in the instrument panel, the consol, switches and all of the interior lights that would be dimmed share a common ground, and one controller.
The ground cluster is located behind the drivers side knee panel; a mass of brown wires.
Just a hint, if your lights aren't coming ON, change the position of the child icon on the center consol.
Happy Trails Beep Beep from Houston!!!
Donald, El Cheapo

[Edited by Donald L. Swinford on 02-12-2001 at 12:24 PM]