why does this fuse keep blowing?

[Tessie McMillan]

Hi folks, does anyone possibly have an idea about this oddball problem? 
The instrument cluster in my '88 80Q no longer lights when I engage my 
headlights.

It used to be that whenever I encountered this problem, I would find a 
blown 10 amp fuse in about the middle of my fuse box and replacing the 
fuse would fix everything. Now, however, I can replace the fuse, but as 
soon as I start the car, the fuse is blown again. I've gone through many 
fuses trying this out -- with various/all accessories turned on and off.

What could be the culprit? The only other 'odd' electrical issues I have 
are that my heater fan is only working on the top heater fan settings, and 
my fuel pump (I think I've replaced it once before) just recently started 
humming. Could either of these cause some kind of overload that is 
affecting the cluster?

Any other way to troubleshoot this?

Tess
in Bellevue, WA USA