Crank but no fire

Hello everyone! So since work is slow because of the beer virus I am getting some more time to work on my car. I have run into a crank but no start issue. I can crank it over by the key and not get it to fire but if I key it on and jump the starter relay posts it will fire right up. The car got a new wire harness and I had someone install it for me. Any ideas where to find the problem? Thank you!