What is it about the clocks used in Citroëns?  They seem to be the first dashboard item that fails.  And while removal of the clock in a DS is a relatively straightforward process, not so on a SM.  Tucked into that sexy way the dash panel tapers toward the center, it requires considerable dashboard disassembly.

SM Interior_2

Be prepared for what you would think to be the simplest of things to be a frustrating experience, as George Klein recounts swapping out SM clock that was recently rebuilt.   In his own words:

Finally fixed a clock that stays working.

So you want to change a clock in an SM.

A comedy of errors or a poor SM design?

Removed the instrument panel, removed the clock. Installed New clock. Clock works OK.

Reinstall the instrument panel. Clock works but not the clock light. Remove the panel, fix the bulb ground. Reinstall the panel. No instrument lights at all. Remove the panel, harness wire was pinched and blown the 10 amp fuse. Try to get a 10 amp fuse. Have many around, but not 10A.

Install new fuse. Check the lights. Lights work.  Install panel. Now clock does not work. Remove panel attach ground wire to clock. Lights and clock work. 2 hours later in a hot garage. So you want to have an SM eh?