I was helping my neighbor today with his Farmall 350. This tractor has been kept inside his tractor shed but hasn't been ran for a while. We installed the carb I rebuilt for him and tried to start it. Wouldn't start. I asked him if he checked to see if the tractor had spark and he said he didn't check it. So here's what we did. First I put an inline spark tester between the plug wire and the spark plug. Cranked it over, - no spark. Next we swapped out a coil from a Super M. Still no spark. Next we put the original coil back on the 350 and got a test light out and turned the key to the on position. When I put the probe on the (+) side of the coil the light lit. I put the probe on the (-) side of the coil and the light lit. I did the same test on a Super M and a Super H he had there. On both of these tractors the light only lit with the probe on the (+) side of the coil, which is what I think it should be. The cap and rotor don't look bad. Is there any other test I should do? If not, what do you think the problem could be?