On my 300d 1985 the electric water pump is not working. Is it supposed to run all the time, or just when needed, if when needed what controls it? I did put power directly to it, and still will not run, so expecting that I need a new one, however want to know how much it is needed, and what controls it. This is my first Mercedes, and just getting it fixed up. It does run well, and the body has little rust.