Bad column?
 

So, last year, my son picked up an 84 C10. As we purchased it, it had a faulty ignition. The PO assumed it needed a new ignition cylinder. I replaced the cylinder, but it still didn't work. After purchasing another column, it fired right up.

Fast forward to today. After the 350 died a couple months ago, he's doing a 4.8L/ NV3500 swap. We hunted down the almost impossible to find hydraulic clutch pedal assembly, and a manual trans column. We finally got all the wiring done and hooked up, but now the ignition won't work. We've double and triple checked everything, and a faulty ignition cylinder or possible bad column may be the culprit again.

What would case a steering columns internals to go bad to cause an ignition failure?

Re: Bad column?
 

If you changed to a manual shift column, you need to look for the neutral safety switch and associated linkage. You may even need to add one as the auto column had it built in to the switch. It may even be located on the clutch pedal under the dash, much like the brake light switch...

Also, check and make sure the rod from the ignition lock down to the actual ignition switch on top of the column is correctly engaged.

T,

Re: Bad column?
 

^ Yup, that right there is the answer. Putting a replacement NSS on the clutch pedal is also excellent safety advice.

Re: Bad column?
 

Several things in a column can cause a no start
Bad ignition cylinder
Worn or broken sector gear
Worn or broken rack gear
Bad or mis-adjusted ignition switch
Bad or mis-adjusted neutral safety switch.

If the cylinder turns, it most likely isn't the problem.
The sector gear is plastic and often looses the last tooth. Suspect this if the ignition powers up but won't power the starter
A broken rack gear usually results in a no-power change when the cylinder is turned.