The shift lockout is a real pain.

To work properly, two fuses are involved (so check them), including the one to the brake pedal for the stop lights. If there's something wrong with your brake light switch, that too will block the shift interlock from working.

And yes, there's a relay involved that requires adequate voltage, especially if your battery is not fully charged (as it might not be in frigid parts of the country right now). But the relay is not easy to get to, especially if you have to crawl under the car (shift linkage) in a snowstorm).

Personally, I have two '93's, one that I bought with the interlock bypassed, so it's like my '84 without any interlock. But I'm still trying to find out how to do the same to my other '93.