On 1973 Chevrolet models, the ignition switch, also known as the ignition lock cylinder, is located on the right side of the steering column, just behind the steering wheel. There are small metal tumblers inside the lock cylinder that line up with the grooves machined into the ignition key. If these become overly worn, the switch will not function.
Disconnect the ground cable from the negative battery terminal. Remove the two screws on the backside of the steering wheel that secure the steering wheel shroud, and lift the shroud and horn contact assembly out of the way. On the base of the steering wheel, use a pencil or chalk to mark the alignment between the steering wheel and the steering column. You will want to reinstall the wheel in the same relative position as you removed it to maintain steering alignment. Loosen the steering wheel lock nut from the steering shaft. Position the lock nut over the ends of the threads of the steering shaft, to protect the threads. Use the three threaded holes in the steering wheel to mount a steering wheel puller. Remove the steering wheel.
Once the steering wheel is removed you must begin by removing the steering lock plate. Push down on the plate and remove the snap ring that fits around the steering shaft. Slide the canceling cam, upper bearing preload spring and thrust washer off the steering shaft. Remove the screw that secures the turn signal lever and remove the lever from the side of the column. Push in on the hazards warning light switch and twist it to remove it from the threaded shaft. Remove the three screws that secure the turn signal switch and slide up over the end of the steering shaft. You do not need to disconnect the wiring harness to access the ignition switch.
Insert a thin screwdriver into the steering column through the slot for the turn signal lever. Insert the key into the ignition switch and turn it to the "run" position. Use the screwdriver to depress the spring latch at the lower end of the lock cylinder. Then withdraw the cylinder from the housing. The lock cylinder itself cannot be serviced. It must be replaced with a new cylinder matched to the vehicle's key if you want to be able to use the same key for all the locks on the vehicle.
Insert the new ignition switch so that the key marks on the housing sleeve are aligned with the key in the ignition cylinder. Place a 0.070-inch diameter drill bit between the ignition key bezel and the ignition switch housing. Rotated the cylinder counterclockwise, while maintaining pressure on the key bezel until the drive section mates with the selector. Press inward on the lock cylinder until the snap ring engages the cylinder and secures it in the housing. Remove the drill bit and check the movement of the cylinder. Then reinstall the turn signal assembly and steering wheel, and connect the ground cable to the negative battery terminal.
