Which way in does the sender unit go?

I thought that . I will just put it down to bad luck/ wear and tear etc. putting it back in now so hopefully have a reading before I go to work

 

The wire work hardens with age the heat and the constant movement, that tiny wire gets hot and causes a bimetallic strip type movement which bends a lever which in turn moves the needle, it's quite complex and clever but very delicate, I think they could be restored to as new, I've been contemplating it for a while, same as the senders, just need a good used one to play with

 

I think putting the wires back to front would melt something straight away as the tank would pick up and earth somewhere

 

Cheers for you help