Manuel Medina, There could be many reasons for engine not to crank. Check for seized engine, use a socket and bar on the crank pulley to see if engine turns fairly easily if it does engine is not seized OK, if it does not turn there is probably internal engine damage which needs addressed. There is a 50 amp fuse under the hood, called IGN fuse check it. You can also check/test or change out starter relay. Ignitions were also a problem in GM's there may have been a recall(you could check this with local GM dealer). Neutral safety switch/plug/wire could be defective or if standard trans. check the clutch switch(test it). If OK. recheck all your connections and installation, have battery and starter tested as may be faulty. Check the attached links, trouble shooting instruction and guides, Good luck.
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https://www.youtube.com/watch?v=TSE0fOrujW0
https://www.youtube.com/watch?v=oCCTL3GbndE
https://www.youtube.com/watch?v=z5DpsRwHTfo