Hi Art.
Happy Holiday for you and yours!

About the cable, on my '93 (and I'm assuming the '91 of this post has a similar interlock), there's a cable (something like a bicycle's brake or shifter cable) that runs from the ignition key's lock to the shifter interlock. You can't begin to budge the shifter free until you've got the key turned in the lock. I think it's more of an antitheft feature, incorporated into the safety interlock. Maybe the '91 has it, too.

I discovered this when, having just bought the '93, I had trouble with my override button (on top of the shifter cover plate) -- when I took off the cover plate, I could see this cable working. There's a little mechanism at the forward (toward the engine) end of the whole shifter box, where the cable (you can see it extending from the forward end) pulls a little plastic piece. Apparently, turning the key in the lock tensions the cable, and you need this to happen in order to release the interlock in addition to stepping on the brake pedal.

Ken