Thanks for the post of the diagram. My moby(12V) keeps burning out brake lights! All my other lights are working fine so I have trouble understanding why such a heavy load is burning out the brake light.
Maybe I will wire all three in the diagram and see what happens. Atleast then it won't die if the brake light goes.
By the way, I use a P21W bulb for my moby, nice and bright. My moby is not using a sealed beam setup though.