Will this destroy my "car's" side window controller?

[FriedMule]

In my cabin scooter is there a button for rolling up and down the side windows, this does only work if the ignition is on.
I have sometimes forgotten to roll the windows up and my remote-key does nothing.

therefore, have I thought of making a simple circuit that sends power to the side window motor and make it roll up the windows.
I had imagined the motor roll up the windows when the ignition is off and the side window electronic is turned off.

will it destroy the electronic to connect an external power source t power the motor when the normal windows power is off?

[Ian.M]

Probably.  Most H-bridge motor drive circuits have back-EMF suppression diodes across the output transistors so your circuit will back-feed the car's switched 12V supply, and the suppression diodes wont be able to handle the resulting current.

[FriedMule]

Hmm I am not sure I get it all, but 12V that runs the wrong way into the original circuit is what I think I understand?

So unless I can avoid both circuit been connected to the motor at the same time, should I forget about it?
A SPST with NC and NO could be the solution?

[Manul]

The correct way would be to switch motor pin 1 to either car controller or battery positive. There will be no backfeeding then. So you just need to rearrange the schematic.

Note: above valid only if motor negative is ground. If not, then you need double pole relay, to switch both motor pins to either car controller or to battery.

[Terry Bites]

 The master window switch in a car does exactly that, no magic smoke.

[jpanhalt]

1) My Ford allows the windows to work while the motor is off, so long as the key is not removed.
2) Wouldn't allowing the windows to work with no key and off make it easier for thieves to get in?  Sorry for my ignorance.  I don't know quite what a cabin scooter really is.  Is it lockable? 
3) Why do you need to power off circuit only to be active when the scooter is off?  Just leave it active all the time and wire it to the battery with an "always on" circuit (cigarette lighter in older cars was always on).  Modern cars call that an accessory circuit.  Cigarette lighters promote bad habits, so they cost extra.