HEY PAUL , YOU ARE NOT TOO SI FI, YOUR ARE DEAD ON, ON THE EXPLANTION, THAT IS HOW THEY WORK, WITH THE SENSING RESISTOR, FOR THESE SYST, NOT TOO HAVE ANY MORE PARTS THAN THEY DO AND REALLY WORK FAIRLY SIMPLE THEY CAN SURE DRIVE YOU NUTS SOMETIMES , BECAUSE THEY SEEM SO SIMPLE AT TIMES I TEND TO THINK WE SEE MORE INTO THEM THAN WE SHOULD ,I CATCH MYSELF DOING THIS AND THEN JUST STEP BACK DO A VERY UNSCIENTIFIC THING GO BACK TO BASICS , THESE THINGS CAN SURE MAKE YTOU SCRATCH YOUR HEAD SOMETIME JERRY