12v Relay on When Car Running

[hotwaterwizard2]

How would I get a relay to come on only when the Engine in the Car is running?
Would I hook it to the Alternator?
The Coil?
There is no electric fan or computer.
I am trying to help a guy on another BB Board.
His problem is:
He has a bad Ignition switch. He wants to install a push button.
But, he wants it to be disabled when the car is running.
His knolwedge of Electronics is limited so it needs to be easy.
Here is what I have so far.

View attachment 36004

 

[Dazza]

This may help. A post from Ante, helping me with my project.

Mud is the word my friend, on some points I can see what you are aiming for. If you want an indication that the engine has started just use the charge indicator light. This takes no sophisticated electronics to achieve. When the ignition is turned on (see picture) the charge indicator lamp gets positive from the battery and negative through the alternator (not charging). When the engine is

View attachment 36006

 

[hotwaterwizard2]

Like This?

View attachment 36009

 

[Dazza]

It looks good to me. But keep in mind I am only a learner. The mechanical side of a vehicle is more my expertise

 

[ante1]

Yes John, this will disable the starter switch as soon as the alternator is charging.

 

[icebox]

can you give an idea on how to shut down a vehicle engine using a relay and switch by a cellphone and where would i put the electronic device to shut down a vehicle engine?. and its schematic diagram ??? ??? :'(

 

[Xenobius1]

I do not know how to shut of the engine with the help of a switch but about the cellphone, My friend has just built a unit which switched on and off when you call.

You will need a cellphone with a  NEW simcard. Remember you will not be able to use the cellphone again as you need to modify it and also you need a simcard which it totally new and which NO ONE knows aout because if somone calls you the relay would switch either on or off depending on the state it was.

If you can afford the rent of the simcard and the cellphone, you may ask again.

The circuit works as follows. when the cellphone receives a ring, it will give a signal to the microphone, only the microhpne is now connected to a circuit to switch either on or off. The circuit also ENDS your call automatically too.

I do not have the circuit but it is easily done because I have seen it and it only needs a flipflop and a 555 timer and some components to aid them.

cheers.