According to the FAQ and several other posts by frequent posters, there are wires for heated mirror glass in all 700's for north america with power mirrors.

I have a 1990 with power mirror, want to upgrade to heated. The door panel is off, and I can't see any extra wires or where they would be.

I also don't understand where the extra two prongs from the glass are going to plug into if there are only 5 wires for the heated setup, as I have been told.

I also don't understand if the defroster wiring is going to need modification, or just a new switch.

Thanks greatly for any help!

************Answered my own question. For the curious:

A closer look at the connector in the door (in the morning light)revealed 5 wires to the connector with the mirror, four on the unheated mirror's end.

So I conclude. The power mirror has 4 wires, the heated one 5. The 5 wires are in the connector in the door, but not in the harness running from the mirror to the connector, unless you have a heated housing and harness.

I'm guessing here, but it stands to logic that the combo switch does the same thing, change to the heated mirror/defrost combo switch and you are upgrading the harness on the switch end to use wires already there at the connector.

So, for any others thinking about this upgrade, you need the housing with a 5 wire harness, not the heated glass like I bought already.

Chances are that any housing with 5 wires will have heated glass installed, unless someone broke their and replacced it with a cheapy from an autoglass place. As of 2006, you can't buy un-heated from Volvo dealer.