Cruise control shuts off with left turn signal

It is HVAC 1fuse #39 in the rear fuse block ,this powers the on/off switch for cruise control ! Fuse Block - Rear Beneath the left rear seat. What engine does it have ? 4.2 L or 5.3 l There is no vacuum involved in the operation of the cruise control ! Your vehicle has electronic throttle control .
Cruise control is a speed control system that maintains a desired vehicle speed under normal driving conditions at vehicle speeds above 40 km/h (25 mph). Steep grades may cause variations in the selected vehicle speeds.
The following are the main components of the Cruise Control System:
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The powertrain control module (PCM)

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The On/Off switch

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The Resume/Accel switch

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The Set/Coast switch

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The TCC brake switch

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The stop lamp switch

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The throttle actuator control (TAC) motor

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The vehicle speed sensor

Cruise Control Engaged
The cruise control system will engage and adjust the vehicle speed based on the activation of the following cruise control switches:
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On/Off

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Resume/Accel.

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Set/Coast

The cruise control switches are located on the multifunction/turn signal lever.
The powertrain control module (PCM) monitors the signal circuits of the cruise control switches in order to determine when to capture and maintain the selected vehicle speed. The PCM uses the throttle actuator control (TAC) module motor in order to control the vehicle speed. For further information on the TAC System, refer to Throttle Actuator Control (TAC) System Description in Engine Controls - 4.2 L.
Ignition positive voltage is supplied from the 10 ampere HVAC 1 fuse to the cruise control switch via the ignition 3 voltage circuit. When the normally open cruise control On/Off switch is turned On, the switch closes and the PCM detects a high signal voltage on the cruise control on switch signal circuit. When the normally open Set/Coast switch is pressed, the switch closes and the PCM detects a high signal voltage on the cruise control set/coast switch signal circuit. To engage the cruise control system, turn the On/Off switch On and momentarily press the Set/Coast switch. The PCM will confirm that the cruise control enable criteria has been achieved. The PCM will engage the cruise control system and record the selected vehicle speed. The PCM sends a class 2 message to the instrument panel cluster in order to illuminate the cruise control indicator. Pressing the accelerator pedal, while the cruise control system is engaged, will allow the driver to override the cruise control system in order to accelerate the vehicle beyond the current set vehicle speed. When the accelerator pedal is released, the vehicle will decelerate and resume the current set vehicle speed. The driver can also override the current set vehicle speed via the Set/Coast switch and the Resume/Accel switch. When the cruise control system is engaged, pressing and holding the Set/Coast switch will allow the vehicle to decelerate from the current set vehicle speed without deactivating the cruise control system. When the Set/Coast switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily pressing the Set/Coast switch will allow the vehicle to decelerate at 1.6 km/h (1 mph) increments for each time that the Set/Coast is momentarily pressed, with a minimum vehicle speed of 37 km/h (23 mph). When the normally open Resume/Accel switch is activated, the switch closes and the PCM detects a high signal voltage on the cruise control resume/accel switch signal circuit. Activating and holding the Resume/Accel switch, when the cruise control system is engaged, will allow the vehicle to accelerate to a greater vehicle speed than the current set vehicle speed. When the Resume/Accel switch is released, the PCM will record the vehicle speed and maintain the vehicle speed as the new set vehicle speed. When the cruise control system is engaged, momentarily activating the Resume/Accel switch will allow the vehicle to accelerate at 1.6 km/h (1 mph) increments for each time that the Resume/Accel switch is momentarily activated, with the maximum acceleration total of 16 km/h (10 mph) over the current set vehicle speed . Momentarily activating the Resume/Accel switch, after the cruise control system has been disengaged by pressing the brake pedal, will recall the previous set vehicle speed that is recorded in the PCM.

If you push on and set and nothing happens, the system may not be working properly.
You can get an owners manual on Ebay.

Did you adjsut the cable on the cruise control? Check the cable and the socket to the cruise control actuator in the engine.

my oldsmobile 1995 cutlass supreme has the same problem, so I replaced turn signal switch.

you may need to change your signal/cruise control device. You may try an auto recycling center.
Remove the positive wire from the battery
remove screws at the back of the airbags. Don't worry, you disable them when you remove power,
With a socket 1/2in drive and maybe an 18 or 20 remove steering wheel
Once the wheel is remove you should see your signal/cruise device.
You could go to your local auto store and buy a book or online www.hayes.com and it will help with the procedure

Check the wiring harness, especially the one that goes underneath the dashboard and steering column. There may be bad wires or loose connections that may have caused your cruise control to act up when turning on the signals or the brights. If that checks out Ok, inspect the speed sensor near the transmission. It may have gone bad.

this is happening because once you shut it off you are sending an electronic signal to transmission and it resets itself once car starts back up as if something inside the ecm has been reprogrammed and erased alll over again. the ecm is your brain which controls your car. get a diagnostic scan ran on it ok?

sounds like a bad body control module for most of your problems, and the brake switch for the cruise possibly.

sounds like problem with switch

Sounds to me that the turn signal switch is bad and will have to be replaced. If you could wiggel it around and get them to work tells me that is wear the problem is.