Not sure what pin 18 to the “trimmer plug” does. From the two wiring diagrams one lead from the rpm sensor goes to 16 which should logically connect to something…otherwise you have effectively disconnected your magnetic pickup. Doesn’t make sense, but hey if it works on your car, go for it.

The above photos sure look like 14-18.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles
97 C280 147k miles