85 300sd interior overhead light

[Mirsad]

I have a 85 300sd. I have a problem with the fuse number 15 which controls the overhead light, antenna, trunk light, door lights, and the sun visor lights. Every time I change the fuse it burns out on me. I can keep the fuse from burning if I keep the interior overhead light disconnected which made me believe that the problem is the actual assembly of the overhead light. I changed the overhead light assembly and the problem was still there. Obviously there is something that causes the fuse to burn out. I wonder where else I can start looking. I already checked if the antenna, all the door lights and the trunk light and everything seems fine. The only things left is to remove the front section of the interior headliner to find out if there is a short caused somewhere else (possibly the sun visor light). But before I do that does anyone have an idea where the short is occurring and causing the fuse to burn?

Thank you