transmission control button

i keep blowing a fuse for the transmission overdrive button which also works the rear defrost. i believe it has something to do with the arm that switches gears on the column. I can put a new fuse in it, but when i switch gears, the fuse blows. I can put it in drive with the car running, put in a new fuse and it will work that way until i put it in park. help please.

i need to find a transmission for a 1966 murcrey montgo can u help me