hello and thanks for the replies!
Here are some more detailed pictures:
A more detailed picture of the frontside
I cant see any indications of which way the diode is supposed to mounted. No dots or anything like that.
The backside (note the red arrows point to where the diode was mounted)
The reason it fell off is unclear, but I think it is because of overheating. I am having trouble with having alternator charging the battery, and I think (hope) this is the problem.
The reason why the holes are so small is that there is still som soldering iron left in the holes.