Restoration of '65 Mustang convertible, A-code engine. The temp gauge pegs to "H" just with the key on, will not come down. New dash voltage regulator, several new temp senders, all of which are "normally closed", so continuity causes gauge to go to "H". The parts books all show only one sending unit, so no distinction between idiot light or gauge. I need a sending unit that is "normally open" so that the rising water temp causes the gauge to rise. Everybody so far has told me I need a new sender, but only one in the books and I've tried four new ones - all do same thing "H" all the time, engine running or not. I need help, thanks.