I used the above link on my E93, and it literally did take no more than 30 minutes to complete.
What's better, I didn't even pull out the A pillar casing. I was able to run it to the side of it, shoving the thin wire to the side of it.
Had a great buddy help me out on the install, and was able to step me through the process very quickly. That's quite helpful as well.
At first, I was skeptical to use the above link, as I was a big proponent of using the connection near the rearview mirror. But in reality, it takes too much longer. Also, running the instal directly to the fuse box means you'll not have to worry about the fuses, ckt breakers, etc
just my .02
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