Mystery fuse

[Fiestaparty]

Hello everyone,

I had the fuse panel under the hood open and found a melted 30A fuse. I found a fuse block schematic that indicates that slot is for the rear defrost. I must have picked a bad schematic because my rear defrost works. I’ve also never seen a Ford circuit protected by a 30A fuse, so I’m guessing a previous owner must have been messing around with something they don’t understand.

My car was being pulled by a motorhome in the past, so they might have run the wiring for the lights through the fuse block. Does anyone else think that is what this fuse slot was being used for?

 

[Handy Andy]

This is interesting, for it is Rear window Defrost, but also from the BCM.

Didn't know if you could have checked (before and after) that when you start the engine on a cold day, the Rear defrost will work for several minutes to help remove fog and frost even when you did not select it.

So next time you start it up on a cold day with some frost, leave the F33 out (no defog selected) to see if the rear windshield will clear on it's own.

You don't select rear defog, you let the system use the "Starting Temperature and warm up" routine it uses on cold startups - if it doesn't clear - then put in that fuse - and try it next time when it's cold-enough to develop frost. See if the Fuse is for the BCM to control it automatically on a cold start, versus you selecting it on the Climate control unit instead.

Ford does this on mine - its' a 2018 to warm up that rear glass - on it's own.

 

[Fiestaparty]

I just finished work and it’s definitely cold enough to test it. -24C. The auto rear defrost is operating as usual. I can see small lines of defining glass on the rear window. The switch to manually activate it is also functional.

 

[Fiestaparty]

Turns out that only the light for the rear defrost was working. The auto feature did not engage after all. Nor did the regular defrost.
Thanks for confirming that fuse is actually for the defrost. Is it supposed to be 30A?