Found this morning that my heated mirrors (both) are not working on my 2001 Tahoe. The rear defroster is working fine. The HTD MIR fuse is fine. I saw posts about possibly needing to replace the mirror glass. Seems strange that both my mirrors would go at the same time but I haven't used the heating function for a while so... Anyway, are there detailed instructions on how to test the mirrors in some way to see what the problem is (before I go trying new glass). Also, if it does turn out to be the glass are there instructions somewhere on how to do the replacement? (Just want to know what I might be getting in to) Thanks in advance.