Well, I had a 70 camaro that had the reverse lights operated by that linkage. So I guess it's possible. You can grab the column right by the dash and turn that collar and see if the lights come on, or move that linkage up and down, does the same thing.
The previous two posts are correct. On a 4 speed, that is the reverse lock out. In GM cars with a floor shifted automatic, that same linkage was used to work the collar on the steering column, since the back-up lights & neutral safety switch was in the column. This linked the floor shifter to the column, as the back up lights switch was NOT in the console like it is on some newer cars. Often times on those cars, like on my friends Buick GS, when his floor shifter broke, he simply twisted the collar like a column shifted car ! On a 4 speed car, this same linkage was used for the same propose, twisting the column for the back up lights, AND serve as a anti-theft device, as you had to put the car in reverse in order to pull the keys from the ignition, just like having to put an A/T in park to pull out the keys., thus "locking" the car in reverse so a potential thief couldn't roll it away. By the time the first clutch got replaced in it, most guys never bothered to hook it back up, usually hot rodders & back yard mechanics. The previous owner of mine actually hooked the back up lights to a toggle switch because he didn't think the factory set up was good enough !! DUH
The factory Pontiac service manual or the 76-81 GM parts manual will show you this linkage as it's supposed to be, the parts manual breaks it down and shows all the missing pieces you are likely missing, AND where they hook to !