? on self dimming rearview mirror replacement

[ctm14]

I need some information on replacing my non dimming rearview mirror in my 2004 X5. I have the clown alarm light and think I have the rain sensor. I am considering bidding on a dimming mirror on ebay that has been removed from an 03 540i. The seller claims that it is compatible with the 04 X5. Can anyone answer the questions below.

1. How can I tell if I have the rain sensor, it never rains here in San Diego?

2. Is the 03 540i mirror compatible with the 04 X5?

3. Is my 04 X5 prewired for dimming or is that built in?

4. How do you do the install?

Here is a link to the auction.
http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW

Thanks for the help.