building LED tail lights

[WS6]

I'm looking to do this for my motorcycle but I am sure it will apply to cars as well. The issue that I am running into is wiring. How can I have the LEDs go from dim to bright just like a normal bulb or factory LEDs? The bulb has a second filament. An LED does not have any filaments. The only thing I can think of is to run an relay. The normally open position supplies power that is heavily resisted to the LEDs. This makes them on but dim. When I hit the brakes, it triggers the relay closed. That then sends power to the same LEDs only with less resistance there by making them brighter. I would put diodes on each power line as well to prevent any back feeding into the unused circuit. How does that sound? I think it will work but I wonder if there is another way. I was hoping maybe someone knew how the factory did it so I could look into that way. I'm worried the factory uses solid state electronics though.



Thanks