Please double-check your wiring.  The red wire is positive and the black wire is negative.

Make sure that you are using the correct size fuse.  Model 148 takes a 3 amp fuse, and all other models take a 2 amp fuse.  Do not install a fuse larger than these!  Doing so will void the warranty.

You can also try bringing the radio to the battery and temporarily touch the power leads directly to the battery.  If the radio turns on, then you know that the radio is good and you need to double-check your wiring.  If the fuse still blows, then the radio will require servicing.