keithw, I can offer some general information about your electrical troubles. The wiring on your truck is very simple and with some patience, I am sure you can conquer your problems..
First step is to locate a shop manual, they are available from Chevy truck parts suppliers or can be found on E Bay. The manual will contain a wiring diagram that will spell out where each and every wire should be connected..
Your tail lites are getting power from the key, they should get power from the head light switch..As mentioned by Mechainiac, your brake lights are powered by a switch . The switch needs constant power on one side, the other side becomes powered when you step on the brakes. That side needs to run to the brake light bulbs..
You may find that your entire lighting system needs to be re-wired. Patching faulty wiring is a frustrating exercise at best..
Look it over wire by wire, figure out where the electricity needs to come from and where it should go..
If you have any more questions, ask here again..
