Take out your mirror glass and see if there is a plug on the back for the heating element.

I didn't know X5s came without heated mirrors, they were standard when I bought mine. There is no switch, the heating is automatic.

I guess if you don't care you could buy the cheaper one and call it a day.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue