your sunroof design might be different from mine. I have a 300D 78 and they use that sunroof cable to retract that sunroof back and forth. my sunroof is barely closing and opening most of the time, but i can hear that sunroof motor kicking in. Mechanic had told me to replace that cable to get that sunroof up to speed, but since i've kept tinkering around with it, i blew out my sunroof motor

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1986 300E 200K + 2 years broken odometer
1978 300D 280K + 2 years broken odometer