Originally Posted by Centretek

In my younger days, my car was protected by an extra ignition coil mounted under the seat. A changeover switch connected the wire from the points to the extra coil, the output of which was bare copper wire stitched into the seat covering while the seat back had earthed wire stitched into it. The switch also energized a flashing LED to remind ME to switch of the "immobilizer".

Originally Posted by mneary

It's probably not going to help much finding your car a few hours or days later. They generally make good use of their time after they steal a car.

You can use the mechanical fuel pump (and presumably carburetor) to your advantage. Put a solenoid in the fuel line before the pump. The car starts normally, but if the solenoid isn't activated the bowl isn't replenished. Thief gets maybe 100 meters and it sputters and dies.

Use something common like the radio controls, running lights, or the cigarette lighter to enable the fuel supply.