Weird starting issue

[Daddy Bartholomew]

1971 GMC 1/2 ton, 2wd, small block 400, 700R4, 3.73 posi. Same owner since 1982, brother-in-law owned it since 1975 or so. Bone stock when I got it, with a 350/350, 3.07 open spool gears.

After years of off and on tinkering, I finally swapped in a tilt column and a tach dash, and immediately afterward the truck won't start until I shift through the gears from Park to Drive and back. Then it fires right up.

Usually. Sometimes I have to repeat the process a few times.

It doesn't appear to be the neutral safety switch; the final position of the gear shifter hasn't changed by shifting it through the gears. It starts out in Park, ends up in Park. But it then cranks and starts perfectly.

I have no idea if it's related, but the instrument cluster now has a Tandem Lock light that comes on when I try to start it. I can get rid of the light (just haven't bothered), but didn't want to start fiddling till I had some idea what is happening.

Any ideas?

[AirSpeed]

Have you looked inside the cab, on the column right next to the floor board? There should be a N.Safety switch, it's a plastic case that mounts on top of the column, it will have wires connected to it of course. It sounds like yours is messed up, you can remove the two screws that hold it on, unplug it and pull it out. Mine was doing the same thing. I bent the tabs that hold the case together and cleaned it out. There are brass contacts in it and a sliding piece that makes contacts for the back up lights and to interupt the starter circuit. Once I cleaned and sanded all the contacts I put mine back together and bent the tabs back down. The switch is adjustable by loosening the mounting screws and sliding it around the column in either direction. You can move it a little and try to start it, if it won't start try moving a little more and trying again. It's pretty easy to adjust.
I bet this is your problem, you may simply need to clean the contacts on the connector. A néw switch is prety cheap if you don't want to take yours apart or if it's beyond repair. Good luck and let us know if it helps!
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[AirSpeed]

One more thought, your switch may have disengaged from the tab on the linkage in the column, there is a little tab that fits into the sliding part inside the switch, yours may have slipped out, that would explain why it starts after moving the lever through the gears, it may be just catching as you move the lever around. You can try loosening the switch and checking if the tab is engaged in the slider. Good luck!
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[Daddy Bartholomew]

That sounds likely, Airspeed. Once the thunder storms go away, I'll go out and check that out. Thanks!