I believe the ignition switch in the regal is in the dash, so it may not be
disturbed by the turn signal switch, but I have no further guesses to
My recommendation, however is to take the car to a shop that can do an
actual diagnosis. If the shop where you took it was able to make the
problem occur longer than momentarily, the should have been able to check
the system for what was occurring.
A scan tool which can read your PCM and BCM may also turn up some codes.
Also try a search of GM tsb's.