I've read that there is a solenoid of some sort on some trucks which is
hooked up to the brale light circuit.

I don't think that is the problem...

I'm trying to find out when the electrical interlock came into being.
I have a 1991 Centurion (Think of a 4-door Bronco) which is based
on an F-350 crew cab for the forward half.

I am having troubles with my ignition switch (sort of)...
I have isolated the trouble to the upper column (the
key turns and does not always move the pushrod that
goes down to the ignition swicth).

I think my trouble with the shift selector being stuck in
park began last night after I removed the lock cylinder.
It seems like it should still be working though... the
lock cylinder went back in just fine, and works like it
did before I removed the lock cylinder.

The clunk sound of the shifter interlock is coming from
the upper column. Is the interlock entirely mechanical ?

Does 1991 have a brake pedal interlock to prevent you
from taking the car out of park? I seem to remember being
able to take the truck out of park from outside the vehicle
when working on it before (memory is not what it used to be).

Anyone got any tips for getting the upper portion of the
actuation mechanism from the key to the pushrod working?
(I think it has a gear in the upper column somewhere).

I am about to pull the steering wheel and dig deeper into the
whole steering column...
I'll check back in a while to see if anyone has had similar experience
I can learn from.

Thanks in advance,
Mark (42) Kanzler