1979 GMC starting problems
 

My 1979 GMC K15 (4x4 automatic transmission) will not start, I thought it was the neutral safety switch, put a jumper in and the truck started right up. I shut it off and it will not start again. I tested the circuit at the safety switch with the key on and had power. Can anyone direct me in which way to go to resolve this problem.

Thanks,
Gene