My '87 did just the same a few months back.  I searched everywhere and
finally found the main light switch to be at fault.  After removing the
switch I took it apart and found all the little contacts inside were
coroaded, covered in green deposits.  After cleaning everything and
lubricating the moving parts I reasembled the switch and it's been working
fine since.  Check your switch with a circuit tester to see if current is
passing through when the switch is in the on position.  You may have this
same problem.

Cheers

Frank

-- 
              *  Frank Condelli  *  Kinburn, Ontario, Canada  * 
                      *  ad793@Freenet.carleton.ca  *