87' Tail light assembly?

Ok, bought some aftermarket tail lights, replaced the old ones, put all the screws back in, and i've got 3 lights and only one set lights up.

I've been having a reoccuring problem with the reverse lights, they will rarely come on, so I'd like to somewhat resolve that problem, and not, it's not the actual bulbs.

Now, as for the middle light bulb (the very tiny one that just pushes into place). I'm wondering what these are for.

Thank you very much.

The reverse lights on my 91 don't come on unless you push the shift lever to the left side of the R on the shift indicator. There is a switch at the bottom of the steering column that can be adjusted. I haven't bothered to fix it, I just give the lever a little tap and the lights come on.