Wish I could be more helpful regarding your issue. I have the opposite situation, if I unlock my 300E using the key in the trunk lock the alarm sometimes goes off. If I need access to the trunk with the doors locked I have learned to unlock the car at the door first.

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'86 300E 5 speed
'71 Triumph TR6
'46 Cushman Scooter
'41 Ford 9N tractor