and the book says to check the fuses in the PDC and in the Junction Block. "The fuses must be tight in their receptacles..."

What specific fuses do I need to check? The little light by the heated mirror switch lights up, but the ice remains on the mirror!

I think somewhere along the line the power is not getting to the heating grids 'cause I don't notice any volt meter deviation when switching on and off.

There must be a relay to power them somewhere. Anyone have any ideas? It's not a big problem, but I just noticed it today in all this ice, and if I got them they just as well work!

 

It is a feature of these trucks to have the heated mirrors fail.
Seriously, it must be because I can't recall anyone saying that theirs worked after the first few years.

 

Mine still do. Easiest way is to check for voltage first. If voltage is present, then the elements went poopy.