im having a similar problem with my b18c. I installed a new aluminum dual radiator, plugged my old fan on to it and it never kicks on. Never. I don't know what it could be exactly causing the overheating. I know for sure there isn't a leak. Also, I just replaced the thermostat the same time I replaced the radiator. How do you go about checking continuity and exactly where is this switch that you keep talking about. Anyone have a real picture of it in their car? thanks for the extra help. I need to get the car down the street but can't.