no spark in 1985 corvette. How to find faulty part?

check the ground wires. see if they are loose if you have to disconnect and clean them with emery cloth.also clean where they connect.

also check the coil see if it is getting fire to it.

Gear on end of distributor could be broke off.

Remove the distributor cap and turn over the engine. Does the rod move? If so the gear should not be the issue. The coil may be bad, or like bandit31 said, wires clean and connected. Is there spark at the plugs? If not, spark starts at the distributor, goes through the coil, and if it goes to a computer control board, that may be the cooperate. Make sure the coil wire is in tight on the cap. May even be a broken wire between the coil and distributor.