The schematic for my Sovereign shows a 50 amp AGU fuse in
the lead between the battery's negative post and the fuse
panel. I found that at some point mine had been removed
and replaced with a large wire nut. Scary stuff.
In reworking that wiring, I used new 4 AWG cable and finally
found a fuse holder and the correct fuses at a local car
stereo shop. Some of the bigger stereos use 4 AWG for power
so the fuse holder I bought was sized to accommodate that
big of a cable. The stereo shop was also was the only place
I could find 40 and 50 amp AGU fuses.
Jimbo / '76 Sovereign