Hi-
I have a 91 740, and my engine reset button is behind a little black rubber plug in the instrument cluster itself, right in front of the speedometer(or maybe it's the clock- I'd have to go outside and check). Of the 2 things sticking out through the clear plastic, it's the one on the LEFT. You have to be really careful when you pull the plug, though, or it can wind up between the clear plastic and the gauges, like mine did...So behind the plug is a black button- push it in using something long and skinny, strong enough to not bend when you push on the button. Good luck- hope this helps.
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1991 745 Turbo :D