Hey, welcome to the forum. My 3811ms has 4 tanks black, fresh, and 2 grey tanks. Like yours they are not labeled very well. I do not know a way of finding what switch activates what pad, under than testing the pads with a meter. But, from what I have found is, if it is cold enough to run one pad you should run them all. But, you might have a unique situation. When we are in extreme cold temperatures I keep the tanks closed and run the heat pads. We have been in -14° no problems.
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