get a electrical schematic for your car, or simply try replacing the fuse box(underdash) with someone elses. (rewire the underdash fuse box??) why would you need to do that ?

Go through that schematic though, check the taillight relay etc.. you will have to look at the diagram. usually fuses are 2 times more then what is installed from the factory. Sounds like though that you have fuses in the wrong places or whatever the hell your doing. or a bad relay now.