If BMW did the same thing as on my '89 E30 you are looking at a separate harness run from a junction box under the dash. I stripped the harness, console and switches, and heated seats from a convertible to use in our '89 325i. Plugged in a new fuse. The harness was a discrete, plug in unit, suspect they did not prewire unless it was getting the heated seats from the factory.
Tom Walrod