Joel, I just turned on my computer. I'll try to help you out.
From the headlight switck , the tail light wire is black/yellow tracer. This wire feeds front parking lights, license plate lamp, front side markers and clearance lamps. also supplies voltage to the radio display. If none of the above are working then I would say the light switch is bad.
There is a blue plug under the instument panel that the wires from the light switch go thru. Make sure it is together good.
The bl/yl wire goes to the back of the truck, there is a 4 conductor plug at the right rear frame rail. Check to be sure it is tight, take apart and put together a few times to see if corrosion has gotton into the plug affecting the contacts. From the plug it goes to the tail lights. Back to above comment, the license plate light is on the same circut. If it is working then the problem has got to be in the tail light light area itself or the plugs just before the tail light. If you have a test light you can check for voltage along the wire to see if it is at the light area. The cheap ones that look like an ice pick and have a short ground wire are pretty good for this type problem.
Other than this, the tail light circut is a pretty simple circut.
Oh yea, I'm assuming you checked the fuse. It's a 20 amp fuse, is #4 fuse.
I hope you already have it going, not sure if this will be a lot of help to you but I tried! GOOD LUCK