I am seeing this alot in the newer cars like the BMW,Lexus and Mercedes. It is a button on the dash that you push to start and stop engine in the car. I know people have done this with their cars but how is it done? I have a 69 camaro with a column key. So how would you wire up a button that would be able to start and stop the engine and how would you do it in conjunction with the key in the on position? Sorry if this sounds confusing but thought this was a cool idea. On the 500SL mercedes they have this button mounted on top of the shifter handle!!

Mark
TOOFUN

On the newer high end cars, the driver carries a transponder, which is your "key". As you approach the car the doors automatically unlock. You get in the the and push the button once, then the computer takes over starting the engine, much like a remote start system would. You can add remote start to any car that has FI and a auto trans, if you have a carbureted engine, and or manual trans it would be difficult to add something like this, as they are made for FI, auto trans cars.

If you take the ignition output off of the key and tap off of it with a wire and run that to a heavy duty push button (or a momentary push button and a relay) you would then wire the output of the momentary switch to the vehicles starter solenoid so it would only crank when the key is in the run position and when the added momentary button is depressed.

Another idea would be to wire up a latching relay to where when it is in one position the ignition is powered up and then when it is in the other position it takes power away from the ignition.

If you are trying to do an engine start and shutdown with just one switch, then it may require a special switch or some kind of sequencing with either relays or something else. I did a Dodge truck a while back and it had no crank position in the key switch on the column and only a start button on the dash and you had to turn the column key to the run position and then push the start button in the dash until the engine started running and then to shut it down you turned the column key back to the off position.

You don't want to design the system to where anyone can start it and like undee72Z stated some cars have systems to where only authorized persons can start the car. If you just wire up a momentary switch for the starter solenoid and retain the ignition key wiring it would prevent someone from easily stealing it.

Jim