If a car is manual and the alternator is not working when the car has stopped you can take the positive or red cable off from battery But with an auto car you can't do that can you If not why not?

The reason is that sometimes a car battery does not have enough charge inside it to start the engine BUT it often will have enough charge in it to keep the engine running after it has been started by "bump-starting" or "push-starting" the car.

But an auto gearbox does not work like a manual gearbox -

it is impossible to bump-start or push-start a car that has an automatic gearbox!

The only way to start a car engine which has an automatic gearbox is to use a good battery to start the engine.

If your car's alternator is not working you could re-charge your car's battery and then it would start the engine ok, even if the car was an automatic.

Here is what you do:

* first disconnect just the +" lead, or both leads, from the car's electrics * then use a household AC battery charger to charge it up * when it is re-charged you can re-connect the battery to the car's electrics and

* it should start the car ok

Another way to get the engine to start is to use a pair of jump-start leads from a good battery in another car.

To avoid burning cables or even a dangerous car fire

Make SURE you ONLY ever connect

"+" to "+"and "-" to "-"

that is

RED TO RED and BLACK TO BLACK

!!!

And it is a very good idea to keep the other car's engine running all the time, to be sure its alternator keeps its own battery charged up!

But the main problem for you will still be this: if your car's alternator is not working, your battery will keep running down fast whilst you are driving the car.

So it a good idea to get that alternator fixed as soon as possible, otherwise you'll be looking for someone to help you use those jumper start leads every time you have to stop the engine of your car!

As you said in your question, if the alternator is not working, so the battery is not being charged, it is a very good idea to take the positive cable off the battery every time you stop the engine. Doing that every time you stop will prevent the car's other electrics (security alarm, dashboard clock, etc.) from running down the battery whilst you are parked. The longer you are parked the more current will be drained from the battery.

So, if you are not able to re-charge the car's battery somewhere by using a household AC battery charger, always disconnect it from the car's electrics until you get the alternator fixed and your battery is fully charged again.