Tail lights not working

First, check if the horn works. If it does, look for the 20-amp "Parking Lamp" fuse. If my diagram is to be believed, it is exactly in the center of the fuse box. Check for twelve volts on both sides of it. That should be a spade-type fuse with two test points on top.

I do not believe the horn has worked at all since i have had the truck. Does that make a difference?

Double checked and the horn does work. When i checked the fuse looks good. But. My multi-meter is reading 0 volts.

Following diagrams on a computer is really miserable when I have to jump between multiple pages one at a time. Without more searching to know for sure, it appears the horn circuit is fed from the same source that feeds the tail light circuit. That is what makes it a good clue.

The problem now is there has to be twelve volts on that fuse if the horn works, unless someone rewired it to solve a dead horn. To save time, pull the light switch out, then check for twelve volts on the orange wire in the connector. If you have it there, we can move on. Turn the switch to the head lights or running lights position, then you should have twelve volts on the brown wire. If it is missing there, the switch is defective. If you have it there, look for anything that does work on that circuit, including the radio display and heater controls. If some things work and some do not, there is a splice in that brown wire that is likely corroded apart.