Rear defroster are not working anymore

Rear Window Defogger not working.
Have gone through many of the steps outlined on various sites.
Big question is -where is the so called breaker for the rear window defrost as outlined in my manual?
The relay is there but where the breaker is supposed to be is a wiring block with a nut in the center to take off.
Is the breaker concealed behind it.
I read of other people taking out the wiring block and finding a power seat breaker but not a defrost breaker.
Any help would be appreciated.
L.B.

Electrical problem
2001 Chevy Impala 6 cyl Front Wheel Drive 154000 miles

1. The rear defroster doesn't work and we suspecting the fuse - but have not been able to locate it. The manual says it behind the fuse box, but how do you get to i?

2. What what cause just the low beam in both headlights to go out at the same time? The high beams work just fine. This is what happened: I was using my ipod with an itrip on trip at night and it the speakers were picking up interference with the low beam headlights on. Then I switched to high beams and the interference went way, switch back to low beam - again there was interference. Then when the car passed, back to high beams (no interference) but when the next car passed and I switch to low beam that the lights no longer worked. I drove with high beams or fog lights the rest of the way.

I will try what you suggested for the rear defroster. As far as the headlight issue. My ipod was not plugged into anything. I was using an i-trip that plugs into my ipod and allows me to transmit my music over through my car stereo.

The headlights are only out on low beam. On high beam they work fine.

Interior problem
2004 Chevy Impala 6 cyl Front Wheel Drive Automatic

The defroster does not work. I repalced the fuse / relay and is not the problem. Any suggestions?

Thank you very much. One of the clips attached to the window came loose / broke off