Stupid wiring and tail lights
 

Ok guys, I'm new here and I will be introducing myself soon. However, I got a big problem. Recently I purchased a 99 Rodeo 2 wheel drive Ls. The stupid thing had issues with the lights and I figured I was smart enough to fix it myself. The left tail light was out and the owner couldn't figure out why. Turns out the bulb was coroded and I just had to replace it. However....I started to look at the lights and realized that not only was that light messed up...but the tail lights in general were messed up. The way I explain this is confusing so bare with me.

When I hit the brakes, all 3 (top, left, right) come on. When I turn my headlights on to drive at night only the right one comes on. It is the exact same light and bulb as the brake lights so the wiring must be messed up. Anyone have any suggestions as to how to fix this?

I just started college, my dad is in the military and is deployed over seas, and the rest of my family is stationed across the country so I am trying to do this on my own haha. I can't affoard to take it to a shop so any suggestions would be greatly appreciated.

My rodeo has this EXACT problem. I'm getting pissed.. Bulbs aren't the issue. I'm hoping its a socket issue and not a wiring issue.