The brown line is the vacuum line that runs to the shut off switch FROM the tumbler assembly(key) sometimes....not often the "ignition" tumbler does not release the vacuum to the shut off switch on the IP which would cause a no start. Like I said, a bit of a long shot but I have run across a few long shots on my journey.

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Rich B

1983 300D Turbo
205k

Excuses are crutches for the weak