I have the same problem with my 2005 Avensis. The fuse which controls the radio, cigarette lighter, mirrors etc keeps blowing. I have found that it is behind the glove box (which has to be taken out by removing the one screw from the side when glove box is open, then spring sides inwards) and on my RH drive UK model the fuse is number 42 at the lowest LH corner of the fuse board. Its a 7.5amp mini blade fuse and is easy to replace. Unfortunately I still don't know why it keeps blowing! There is a clue in the fact that when I plug anything into the cig lighter, the fuse blows, although it also blows sometimes without this!
ray, June 2013