Random electrical issues

For the past couple of years I have had a random issue where my radio will cut out and
flicker off and on then the gauges will flick back and forth with it occasionally causing a
loss of power.  After the first time it did it I went about a year and half without it doing it
again then it will do it one day then go months without doing it again with no real rhyme
or reason found for it. I have taken it to numerous shops and not only have they been
unable to find out what is wrong with it but It seems to be happening more often now. I
gave in and took it into the dealership last week to have them look at it knowing that
typically they would be the more expensive option and after looking at it for about four
hours and not finding anything they gave it a clean bill of health. Since then it has
acted up twice in a week. would be thankful for any ideas that can be come up with.