'93 civic HB dash lights intermittent on/off , common prob ?

my '93 civic instru=met lighting in dash board go on and off intermittently
but are off more than on and i can not find the trouble is this a common
familiar problem to anyone.

occasionally riding along and they come on then 2-30mins - 2 hours later
(random) they will be off, when they are on i can adjust brightness with
dash light dimmer switch. i tried wiggling wires, banging dimmer switch,
and looking at fuses in fuse box swapping for new one etc and nothing seems
to produce the desired Cause/Effect need to diagnose and fix.

any ideas ?

rob