Some of those trunklid-mounted switches have the capacity to be left engaged...in other words, to stay in the depressed or light off position. Also check the wires plugged into the back of the switch....that's what my problem was. When doing so, though, be prepared to break at least several of the small clips that hold the trunklid lining in place...no biggie, they're very cheap.

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Best regards, Michael
'92 500E
'88 300TE