I was replacing my battery on my 1984 300cd and the plug that comes from a wire behind the battery and has a three pin plug that plugs in along the firewall in the middle came apart and the plastic sleeve that holds it to the other connector crumbled. The car still runs but what is that for?
Thanks for your help in advance.

__________________
1982 300TD
1973 220D ambulance
1974 240D pick-up