It may be bad contact not the microswitch. Have you tried cleaning the contacts on the visor clip and the tip of the visor? That is where it get +12V. The ground is from the screws which hold the visor in place, chean that too. Or check the fuse.

Easy way to check is to put 12V on the visor and flip the mirror cover.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.