Okay I have a 2005 Chevy Impala. And I am wanting to take the old fuse box that is under the hood out and replace it with another one. Which wires do I disconnect in order to do that

SOURCE: Assumed blown fuses - looking for fuse panel on 2003 Chevy Impala

I don't know about the rear defrost, but there are 2 fuse boxes inside the car. Just inside the doors on the far sides of the dash. The covers sit between the dash and the doors. There are holes to stick your fingers in, and pull the covers off.

The fan issue, may be different then the prob. I had, I didn't have speed 1 or 2 on mine.
I don't remeber what the part is called, but it's some resistor board deal, that sits up under the dash on the Pass. side, right up against the firewall, it's a pain to get the new one in, once the old one is out though, so be careful not to crack the board. Ask a dealer, they will know what it is. I think it costed me like $30.
I hope that helps.

SOURCE: keeps blowing 15a efi fuse 1991 toyota pickup 2.2 re

there's a short somewhere causing that amperage to go up

SOURCE: Cruise control stopped working

if the fuses are ok then i would say that there is a distruption between the cruise module vehicle speed sensor and the computer(ECM). unfortunately this is something only a qualified tech with diagnostic equipment can correct. i'm sure there are stored fault codes that the tech needs to check and reset. it's been my experience that oftyen times when this problem happens it has to do with the transmission control module which dictates how the engine and the transmission sync up to shift properly and your speed is measured through the transmission circuit thus the cruise control circuit is slaved to that.anymore questions feel free to contact me . just click my user tab on this site

SOURCE: Can not find 2000 Chevy Cavalier Flasher Unit

the relay unit is under the dash near the steering wheel should be connected to the searing shaft it looks like a small square green or black the relay is about 35$

SOURCE: diagram for under hood fuse box

YOUR FUSE BOX UNDER THE HOOD IS LOCATED BESIDE THE BATTERY RIGHT SIDE THAT IS AWAY FROM THEWINDSHEILD, ITS A BLACK BOX RECTANGLE SHAPE IT HAS A COVER OVER IT SNAP THE COVER OFF AND YOU WILL SEE THE FUSES