A question on using potentiometer as a variable resistor
A good rule of thumb is that the maximum wiper current (if not stated on the datasheet) is the lesser of the current when passed through the entire element would reach the maximum power dissipation for the pot and 100mA. 

So if you have a 10K 1W pot, then the maximum current would be 10mA, and the minimum resistor value that would be safe (at 12V) would be 1.2K.  

That's a conservative figure suited for carbon and cermet pots- pots that designed for use as rheostats (eg. some wirewound types) can handle more current because they have a thermally conductive core attached to the element to spread the heat.