The plugs don't turn "off" with the light. For about 15 seconds after the light extinguishes, the plugs continue to heat up. Some have found the car starts better starting it 15-30 sec after the light goes off because more heating has taken place.

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'81 MB 300SD, '82 MB 300D Turbo (sold/RIP), '04 Lincoln Town Car Ultimate

Sooner or later every car falls apart, ours does it later!
-German Narrator in a MB Promotion Film about the then brand new W123.