Early cars have a 3 pin white connector, designed for the auto dipping mirrors. Same basic functionality, but with a different connector. Yours should be 6 pin, I seem to recall it being black on the later cars...and they're usually well buried. I confused mine for the IR keyless harness when first digging around for it.
If it's a BMW mirror, it should use the same button. My car has a gentex out of a maxima. Cost me $10 and has more functionality than the factory units of the car's vintage, but I had to pull the old button and replace it with a universal one.
best, whit