1940 ford

First determine if you have current to the coil with the key on. Use a test light or take a small jumper wire connect to the plus side of the coil and scratch it briefly to ground. If no spark present you must get current to the coil first. If you do have current to the coil then get a pair of insulated pliers remove the coil wire from the distributor cap and using the insulated pliers hold the coil wire near a ground source like the engine block itself. Crank the engine and check for spark. The spark should be blue in color and snapping. If yellowish and weak with little or no snap then some ignition work will be required such as possible points and condenser. If spark is good reinstall the coil wire and remove spark plug cable from the spark plug and hold near ground (same test as coil) and observe for spark. If no spark then either cap or rotor problem. If you need further help just ask here.