Did they really have microprocessors in 1986? Dumb question, but did you check the actuator switch? The switch you press to activate the top mechanism. The mechanical switch is a moving part and it is far more likely to fail intermittently than a none-moving "solid state" part. I have a 1991 300sl and the top contoller has a pair of relays which carry most of the current and "interlock" with the window up/down contoller. Solid state devices don't fail intermittently. You most probably have a bad switch, bad or corroded connector, or a bad relay. It's a complex system, but a a logical trouble shooting approach is more effective than just throwing new part$ at the car until it works again. Tod

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