fuse blowing on 5KT

[millers ink]

hey,
i thaught i fixed the problem with #12 fuse blowing, but it did it again
today.
i found a corroded back up light socket, and when i unplugged it, the
fuse didnt blow.
that was about a month ago, and today, it blew again.  as you know, it
kills the speedo, tach, and all indication, as well as the one backup
light that i still had.
one thing that i did notice, was that today, after a sprint down the
highway, there was a rather loud buzzing from the rear of the car.  i
thaught it may be the fuel pump, but didnt look too much since the car
was working perfect.  when i got home, the tach had stopped (fuse
blown), and so had the buzzing.  i dont think that #12 has anything to
do with the fuel,. but i am out of ideas.  i have a manual, and it shows
that the fuse should be a 5A, but the cover of the fuse box shows 15A.
i had a 15A in it when it blew, and when i replaced it, i only had a 20A
in the car, so i crossed my fingers and it worked for about 20 minutes,
and then it blew.  the car still runs well, so it is not leaving me
stranded, but i dont want to change any more fuses until i actually into
check some of the possible causes.  any insight here would be greatly
appreciated.
later
brian
87 5KT with 226000KM (today)