INPUT_PULLUP. Connect pin to 5V or Gnd?

mjosbesh:
My limit switches are also connected w/ INPUT_PULLUP. Is there any way the limit switches could malfunction if I'm grounding to the aluminum body of my project instead of grounding to a grounded pin of the arduino? My project is a motorized TV mount btw.

The arduino ground needs to be connected to the aluminium body to make the circuit. It's just how electricity works.