i have an 04 mcs, what is the bottom rear bulb on the taillights for? the top is the park and brake light from what i can tell, and the middle is the turn signal, I cant figure out the bottom one though...

 

ok i think i just answered my own question, the spare bulb which is on the bottom is for rear fogs, which mine is not wired for. the previous owner who put in these after market altezzas that im removing, must have got them switched around because the brake bulb is supposed to be on the bottom? is this correct?

 

Yes. You can also make both the top and bottom lights come on when you brake. Do a search for Brakelight Mod.