Blown fuse problem solved
 

My car is 1979 300sd (116).
A little history of my problem, the brushes of my heater motor went bad. I replaced the motor with a brand new motor, it then blew fuses 3 and 9.

I got a new replacement motor, It still blew fuses 3 and 9.

After pulling out my hair for a few days, I bought a used motor...now it works.
no more blown fuses.

The used motor I bought looks like an orginal Bosch motor built in Germany, the replacement were Bosch motors built in Brazil.

I thought I would pass along this info for any one else that ever has this problem