Which filament is for brake lights on 2002 Chevy Express 2500?

A 2002 Chevy Express 2500 uses a dual-filament bulb in the taillight assembly for the brake and running lights. There isn't a separate filament *just* for the brake lights. One filament is for the running lights (tail lights), and the other is for the brake lights. When the brakes are applied, both filaments illuminate – the running light filament and the brighter brake light filament.