Conversions & Hybrids - LS1 not starting

put ls1 in 72 chevy truck with s&p wiring harness. getting fuel but no spark. What can cause a no spark problem

Is the Crank position sensor plugged in? It is the sensor above the starter. That is the usual suspect.

Make sure that the wire that you have hooked to your switch is hot in all the positions it needs to be.Mine was hot with the key on but when I started to crank the engine over the fire would go out and it would not start.

thanks hugger you were right on the problem props to you thanks fired right up