Fuse #15 is blown, and blows instantly when replaced (with the proper 8 amp white fuse). So there is a dead short. I confirmed that the red (positive) wires leading away from fuse #15 are grounded out, in other words, in direct contact with the chassis (negative) somewhere.
Fuse #15 provides power to: the trunk light, the INterior lights, the door lights, the power antenna, and the "warning monitor term. 5". (BTW, what is the "warning monitor term. 5"?)
A Mercedes mechanic suggested that a short in the Power Antenna is typically the culprit when fuse #15 keeps blowing like this. But my power antenna checks out working properly; and even when the power antenna is completely disconnected from the car, the dead short in fuse #15 is still there.
So...I am stumped! Any prospective solution much appreciated.