The rear headrests are partial electric and partial vacuum controlled.

mattd,
Maybe you can spot a cause for the short near the switch (take out the front courtesy light) or motor in the trunk (behind the left upholstery panel)...

NoDubs,
Have you ever tried to change the switch?

greetingz,

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1990 300SL-24
1993 C250D with a minor 600+k kilometer
www.MBenzNL.com(the Netherlands)