Battery Wire

Had a weird occurrence today. Vehicle has been perfectly normal, but after I shut the car off upon getting home from church today the car wouldn’t lock or restart. I went loosen/retighten the battery connections and the corrosion caused this small wire to the negative terminal to break off. Strangely, after it broke the car started working again. What exactly does this little wire do. Is it bad to run the car with it disconnected if it’s working?
Thanks!

 

Picture 2

 

i'd guess it goes to a battery sensor and eventually the ECU

 

Yeah! It's not there for looks! Loosening and retightening your battery terminals isn't going to do anything. You need to do some battery terminal maintenance! Those things need to be soaked in baking soda and water to neutralize the acid, cleaned and brushed, battery posts neutralized in the baking soda solution, cleaned and brushed, and finally while you've got both sides disconnected, solder or bolt that wire back onto the terminal. I can almost guarantee that the problems you're experiencing are due to the sorry state of your terminals.

 

Welcome.

Scary looking battery terminal!

 

That wire goes to the engine to insure a proper ground to the starter, alternator and other electrical components, it definitely needs to be reconnected because the ground wire to the body may not be enough to insure proper function of the electrical system, that's why Toyota has that wire as part of the electrical system!!

Also that corrosion is what damaged that wire, after cleaning it up properly and adding anti-corrosion compound/spray be sure to inspect your battery terminals at least twice a year to avoid this happening again, you're lucky you weren't stranded out on the road.

 

This^