1998 Chevrolet Express

Greetings all,
On my 98 Chev. Van, V8 Vortex 350? 135,000miles. I am experiencing a strange(for me) electrical problem. Whenever I put 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 the blinker, but that is as far as my thinking goes.
August 26, 2007.

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