Hi Dominick,

The pictures below show what I found when I opened up a 3 way switch.  I want to install a dimmer on this switch, and I only see 2 red and one white wire coming from the box to connect to the new switch.  I do see some black insulated wire on the inside, but there is no black wire coming from the box to connect to.  It looks like maybe there is no ground also?  My questions are which red one do I connect to where on the new switch, and how important is it that I add a grounding wire when installing the dimmer switch?

Thanks.

Tom