Turns off and on

While all of the above solutions may sound logical, it's been my experience of 30 years dealing with Electrolux that the problem is most likely the thermostat attached to the motor housing. The reason the vacuum shuts off and on is the motor is too hot. First thing you'd want to do is check for a clog in the hose or powerhead. Simply remove the hose from the vacuum inlet, drop a small coin through it. If it comes out the other side, no clog. Secondly, remove the metal wand from the power nozzle and look inside for a clog. Remove the debris if so. If both of these are clear, the thermostat needs changed. I've had the same symptoms hundreds of times over the years and either the thermostat is itself faulty or the motor is bad. If the motor is bad, you'll hear it when the vacuum is running as it will be oddly noisier than when it was new. The thermostat kicks in as a safely precaution so there is no "meltdown". If the motor sounds normal then most likely the thermostat needs changed. Sooo, there you go! Hope it helps.

The on/off switch is defective and shorting out. Left alone, it could cause a fire, so replace the switch.

The on/off switches in these machines normally do not short out.
If it turns on and then off and back on, it sounds like there is a short in plug. Electrolux's are prone to having loose prongs on their plugs. Usually causes an arc at the plug and can be dangerous but if it isnt' arcing chances are it isn't your plug.
or
I have seen where the front cover was lose or not closing properly. In turn the machine turns on and off repeatedly, especially when being lugged around. There is a little pressure switch where the bag sits that disables the machine from being operated without a bag. If this is not being compressed all the way, the machine will shut off but as soon as you compress it, the machine will reactivate to on. In turn, causing this to be the issue.

To diagnose this is pretty simple.
Make sure you have the correct bag installed Electrolux C Bag
Make sure the bag is sitting in the chamber correctly
Make sure the pressure switch in the lower right hand side of the bag chamber moves freely.

If this all checks out turn the vacuum on it's end with the hose end pointing up. Turn the machine on, then connect the hose. Then wiggle the hose while connected putting a slight strain on the hose to see if the front cover is moving or if the machine is turning off.
If this reproduces the issue there is a fault with the pressure switch activating too soon or the front cover is not sitting closed correctly.

Another issue could be a short in the contacts in the cord reel. To diagnose that is to plug the machine in, and turn on. If the motor is running, slowly retract the the cord back into the machine while running, if the machine turns off while retracting, there is a short either in the cord or in the contact point in the rewinder assembly.