your brake light is probobly not connected, if it's the red colored brake light, there's a sensor/switch that senses that could be broken. most likely it's a ground, if it's that wear sensor it's either a ground or a wear sensor making contact and you'll need brakes soon. when you say shifting issues... Is it a flair, slamming into gear, taking it's sweet time etc?

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hum.....
1987 300TD 311,000M Stolen. Presumed destroyed