When exactly does the idiot light come on? Right on start-up? Or later?
The thing about the system that's not in the manual is that the idiot light only comes on when the circuit with the bad bulb is energized, and not before.
What I'd recommend is to start the car and keep your foot off the brake. Is the idiot light on? If so, there's something wrong with the warning circuit itself. If not, then hit the brakes. If idiot light comes on then, look carefully at the brake lights. If not, turn on the headlights to the first click. If idiot light comes on, look for a bad bulb in the running lights, license plate lights, etc. And so on.
I've had a time tracking down a bad running light on the SIDE of the rear light panel. Just work through it logically and you'll figure it out.