Three days ago, I noticed problems with my dashboard lights and dimmer
switch.

While driving, I switched my interior lights on for night conditions, only
to have my entire dashboard and clock lights drastically lose their
brightness. I tried turning up the intensity using the dimmer switch, but
the interior lights would only increase brightness marginally. When I
turned the interior lights off, my odometer light went back to its
original brightness.

I repeated the process above several times, but the condition persists.
Since then, I've checked all of the fuses in all three fuse blocks but I
couldn't find anything wrong there. I'm guessing that there must be a
short occurring when I switch on my interior lights, but I'm open to any
other suggestions. If it is a short, how can I find it and fix it??  

Additional Info:
I turn on my interior lights by twisting the control knob on the end of
the signal-light lever. This is the same lever that controls the high/low
beam headlights and is situated to the left of my steering wheel. My
dashboard and radio lights dim out when I have the knob set to the
interior lights position and when it is set to the high/low beam headlight
position, but all is normal when the knob is set to 'off'.

Thanks for your help!!!