I know what you're thinking. It's the rear sliding glass to blame, right? Well, I think that's not it. For one, I never use the rear sliding window. The problem is the light on the button for the rear defroster/outside heated mirrors doesn't even come on. I assume if the rear window connection was a problem I would still see the button lit up?...or maybe not.

So far I've swapped all the fuses involved (fuses listed in the owner's manual that relate to the heated mirrors and rear window defroster) and also swapped the relay in the fuse box (high power relay that is noted as being related to the heated mirrors/ rear window defroster). I took the back seat out just to have a look at the wires and everything looks perfect. I NEVER use the rear sliding window because when I bought the truck new in 2014, I had already read about the problems people had with the defroster when they use the rear slider a lot. I did however go ahead and open/close it a bunch of times in case the contacts weren't making good contact. From what I can see, it looks good and I can even still see some of that factory lube they put on the contact area for the rear slider. So, I 'think' it's not the rear window that's the problem.

Any other ideas or troubleshooting tips?

Just looking for some more ideas that I could try, if any, before I give up and pay the dealer later this year to tell me what the problem is (then I can decide to fix it myself, if I can, or have them do it). It seems like such a trivial thing, but come wintertime, I really need the heated mirrors to work.

Truck is a 2014 F-150 XLT SuperCab EcoBoost 4x4 with 302A Equipment Package

 

I noticed another discussion about this subject here in the list of recent discussions. I read through that and I may be out of luck because it looks like there were a lot of ideas there that I already tried and if I can't find an obvious cause for the problem myself, then I'm stuck with asking the dealer to troubleshoot it and tell me what the problem is for sure (then I decide whether or not to fix it, depending on the cost).

It's a shame, for such a simple thing, but something I need/use OFTEN in winter and even not during winter on mornings where my mirrors are covered in dew.

 

Mine is doing the same thing and like you have check fuses and relays with no luck. Have you gotten yours fixed yet? Would be nice to know what you found out. Thanks in advance. Cruiser

 

MyMine led is doing same thing ! Same truck also