A knob placed on your steering wheel allowing you to drive with one hand, leaving the other free to put around your date.
Keith's put a suicide knob on his steering wheel so he could have one arm around Caroline while he is driving.
A knob attached to the rim of a steering wheel that enables a driver to turn the wheel by moving the knob. Very common in the late 1940s and through the 1950s. Illegal in most places since then. Also called a nigger knob.
Ermal has a suicide knob on the steering wheel of his Case tractor. He decided to put one on the wheel of his Pontiac, too, so he could spoon with Ida Mae while he drives.