1972 c10 ignition switch problem..?

[I_Wanna_Go_Fast]

Hey guys
Looking for a little help from the wealth of knowledge on this forum..
I have a 1972 c10 that I've built far from stock.
IT was originally built to haul my dads track car to and from the track. I now have it and have turned it into a street/strip truck.
built 489 bbc, th400 with manual valve body and a bunch of other goodies.

A problem surfaced towards the end of last year during a drag and drive I was competing in.

If I start the truck when cold, let it run for a bit and shut it off, everything is fine. If I drive it a while (an hour or more), when I go to shut it off it will act as if the ignition cuts off for just a second and then stays running. Its definitely not dieseling as others have experienced on here.
If I grab the end of the key and jiggle it around and try to point the tip of the key towards the floor, it will shut off.
I'm leaning towards a wore out ignition switch but wanted to check in here and see if there were any other possibilities.

I cleaned up most of the wiring on the truck - didn;t cut any wires - just removed the unneeded stuff like the emissions, etc.
There is no vacuum stuff on the truck and no HEI or anything like that.

Any help is greatly appreciated.
Thanks!

[RustyPile]

It's hard to say without knowing exactly the mods you have done, but symptoms point to ignition switch failure.. If you have a high current aftermarket ignition system, you can take the load off the switch and install a relay...

[I_Wanna_Go_Fast]

I did put an MSD 6AL ignition system in it.
I put a fused terminal block under the dash - it has 6 terminals.
Power supply to this terminal block comes from the unfused switched ignition power terminal on the factory fuse block. This was to power things like the MSD box, the tach/shift light, relay for electric fans, fan for trans cooler, new radio (retro sounds), etc.
The MSD box is powered directly from the battery, the switched ignition is only the trigger to turn the system on.

I leave for Sick Summer in a few weeks and am hoping to get this ironed out before then

Thanks again!!

[dmjlambert]

Before shutting off the engine, pull the fuses in your accessory fuse box except the one for MSD and see if any of those accessories are keeping your engine going when you turn off the key. If any of those items are the culprit, switch power to that culprit with a relay like you did for the electric fans.

[Wrenchbender Ret]

I have a low mileage 72 & the ign. switch failed a while back. The starter stayed running after you return the key to the run position. It sure sounds like that is your trouble. They are not hard to replace unless the connecter is burnt. Then you have to replace the pig
tail.

george