PMFJI,
Let me throw another concept out since you guys are really close to getting this stuff sorted out.
One of Ohm's buddy's, Kirchoff developed a law used in circuit analysis that says the sum of all the voltages around a circuit must always equal zero'.
In the heater motor circuit that means that if the battery is supplying +6V then the fan motor must have -6 volts across it's terminals. If we have a resistor in the circuit then we must have some combination of voltages between the resistor and the fan motor that equals -6V so that the sum still remains zero.
What happens with the resistor is that you can control the voltage dropped across it by changing it's resistance (our buddy Ohm's law). i.e. if you could make the resistance infinite (open wire) then all of the voltage in the circuit would be 'dropped' acrossed the terminals of the resistor.
If you reduced the resistance to zero (short circuit) then NO voltage would be dropped across the resistor and the fan would 'drop' all of the available 6 volts from the battery.
With the resistor at some mid-point, then some fraction of the available voltage will be dropped across the resistor and the remaining will be dropped across the fan motor. When you switch a varible resistor, you are changing the resistance of the device which changes the voltage drop across it.
Bottom line is that all of the available voltage from the battery MUST be dropped by the rest of the stuff in the circuit (i.e. resistor + fan motor) in order to obey Kirchoff's law.
Bill, I'm a veteran of USAF electronics schools to but my work was so secret I didn't even know what I was doing.
