I haven't looked at my X3 closely, but there is usually a rubber boot over the wire bundle. You are looking for signs of chafing at either end of that boot. You may need to take the trim panel off to see better. If there is no visible damage, then it is likely the switch. I would diagnose it properly before throwing parts at it; doing so is nearly always the most expensive way of trying to fix something.

Jeff

__________________
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