7. Miscellaneous

IGNITION CUT-OFF SWITCH

Here's a simple relay circuit that you can use to insure that you don't forget to set the switch when you turn the car off. It automatically sets itself: 

                              Double pole                                      
                          single or double throw                               
                          normally open (N/O) relay                            
                                                                            
   Key switched                  | :/                               To ignition
   Power    >-------o----------- |/:  o-------------------------->   switch    
                    |            | :/                                starter   
                    |            |/:  o-----|         /              pole      
                    |              :        |       /                          
                    |            Relay      o-----/     o---------|            
                    |        |--- coil------|        ^            |            
                    |        |                    Hidden N/O      |            
                    |        |                    pushbutton      |            
                    |     chassis                 switch          |            
                    |     ground                  to enable       |            
                    |                             starting        |            
                    |                                             |            
                    |---------------------------------------------|
The left side of this circuit should get its power from a source that is hot with the ignition is in the "on" position, and cold with the ignition turned off. When ignition switch is turned on, power is not supplied to the starter switch, preventing starting. When you press the hidden momentary button, power is supplied to the relay coil, which closes the relay. This supplies power to the ignition switch through one pole of the relay, while supplying power simultaneously to the relay coil through the other pole, keeping it latched so that you can let go of the pushbutton.

When you turn off the car, power is lost to the relay coil, which then automatically opens and "arms" the system. A variation of this circuit is to use the electric fuel pump power supply as the input, and feed the output to the fuel pump.