car won't start until I release the key from the cranking position.

Hi guys,
73 Duster, 360 , stock dizzy, chrome box.
Flame thrower coil.
I can crank and crank but it doesn't start till I release the key from the cranking position.
Where is the best place to start looking?
The switch?
The harness?
The ignition box?
I have a FBO box I could try if anyone thinks that could be an issue.
It doesn't matter how long I crank, short-long.
It always starts, just not when cranking.