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Date registered: Oct 2002
Vehicle: 1967 250 SL, 1963 220Sb
Location: Los Angeles / Altadena
Mentioned: 3 Post(s)
Quoted: 102 Post(s)
Trunk locks were an option on almost all Benz. By any chance are you using a different ignition key to start your car? The "valet" key will unlock your doors and start the car but will not engage the vacuum unlocking system.
How odd. Definitely not the case with later (W123) Mercedes vacuum locking systems. If vacuum fails in the later cars, gas door defaults to unlock (and can't be locked). The idea of the valet key not operating the vacuum system seems very strange to me as on the later cars the vacuum switch for locking and unlocking is based on the lock button position of the driver's door lock, which wouldn't know if you used a master key or a valet key.
Currently: 1967 250 SL, 1963 220Sb, 1965 300SE Lang, 1971 280SE parts car, 1972 Alfa GTV, 1965 Alfa Duetto, 1993 BMW R100R
Past: 1971 250 C, 1985 300 TD, 1967 250 S, 1968 280 S,1981 300 D, 1982 280CE, 3 Facel Vegas, Borgward Isabella Coupe, Alfa 2600 Sprint, Volvo P1900 (yes), numerous less interesting Volvos, ...