Coincidence, I was just thinking about this thread again yesterday. And I got to thinking, if the top portion is only the tails and no brake light/ blinker, then that means it must be only a single filament bulb, like 1156 instead of 1157 (for example). If so, that means you could not just splice a wire or something because there is nothing for the circuit to light. So the only way would be to install a bulb socket that is set up to hold a dual filament bulb, which has an extra wire coming out of it. It shouldn't be difficult because the sockets would be the same size. But I think that's what we're looking at here. The good news is that once that was done, all you'd have to do is run the lower brake light wire to it (splice), there would be no need for a relay or anything like that IF you first made sure that the fuse is okay because the current passing through it just doubled (well, not double if the 3rd light is also on it). I imagine upping the fuse 5 amps from 15 would be okay, but would worry about adding 10 or 15 if that's what the circuit now required. In that case I'd want to run a new line, new fuse, and perhaps relay if necessary. But before I went through all that I'd probably want to go LED. But I really wonder why the hell Chevy didn't do it right in the first place!!!