Why would cause the engine light to come on and stay on in a 1998 chev silverado 6.5 turbo diesel1/2 ton truck? why would the horn toot by itself?

Sounds like two seperate problems. Horn switch is sticking for some reason.(spilled beer in steering wheel ; ) the engine ligh could be a dozen different reasons. There are 15 different sensors that read what's going on in the engine from oil level to position of the gas pedal to temp of coolant to air fuel ratio and if a sensor is getting a bad reading or is broken the engine light will come on. When it does it stores a code in the computer that can Be read with a diagnostic tool. They will do this for free at most parts storeS. This code tells what sensor is bad or getting a bad reading and you can go fro there.hope that helps a little