Texvan

Greetings all,
On my 98 Chev. van, I am experiencing a strange(for me) electrical problem. Whenever Iput the turn signal to the left position, and have the headlight switch either with just the parking lights or the headlights on, the blinker stops. When I am driving with the cruise control on,(lights off)and turn the left blinker on to change lanes, the cruise control turns off. Sometimes, when I have the turn signal in the left positon and apply the brake, the blinker turns off. It won't be a bulb, because it works sometimes. I have had it to a local shop (not the dealer yet) and they said everything worked for them when they test drove it. Can anyone make any suggestions, please. I am thinking some kind of short in theblinker, but that is as far as my thinking goes.
Thanks,
Jim