How do I solve electrical problems with dash mounted accessories?

We recently bought a 2001 ford expedition XLT and have had no problems until today.  This morning my wife drove my daughter
to school (about 15 miles), along the way the parking brake light came on.  When she got to the school she shut off the truck and
the heater blower motor stayed on.  She turned the truck back on and off and the blower motor continued to run until she shut it
off at the heater control switch.  I ran into town to check things out.   I set and then released the parking brake which turned off
the parking brake light.  The fan problem was no longer happening(was working correctly).  I checked all the brake lines and the
parking brake, all were fine with no leaks.  On the way home the low washer fluid light was flashing on and off and the radio quit
working.  The radio turned back on as soon as I put the truck in park and the washer fluid is full.  I have had similar problems in
my 2000 F150 XLT with the radio and instrument lights and occasionally the power window.   This must be a common problem.  
Has anyone else had this happen to them?  Does anyone know what the solution might be?