93 2500 Chevy truck won’t start

Specific vehicle/engine information (4cyl, V-6, etc.) is often very useful in helping to provide information:) There are so many things:) Is it even cranking the engine? Does it sputter or try to start? Did you change all of that because it won't turn over or because when turning over it won't start? Follow this and you should locate the problem if the engine is cranking. If it's not cranking, you have the Ignition switch, relays, solenoid and battery cables/clamps to consider. Make sure the battery is fully charged. Ignition systems require a minimum amount of voltage and start best with a fully charged battery. Fuel, check fuel pressure to make sure the fuel pump is operating and that you are getting fuel to the injector(s) with the correct amount of pressure for that engine/vehicle. Spark, you need to verify that the engine is firing at the spark plug and that it's doing it at the correct time. (timing chain/belt issues) You need to verify the engine timing, this can be done by checking that the engine is at TDC (top dead center) when the rotor is pointing at cylinder 1. Air, make sure there are no restrictions and that you have a filter that allows air to pass freely. A quick test of the timing system to make sure it's intact when you have a distributor, is to watch the distributor rotor rotating as the engine is cranked. If it's not moving, you have a problem with the timing chain/belt ot the distributor.