How to completely turn off device when float switch is open
You're doing this the hard way.

First off, R3 is not your problem. 12 volts / 240k is 50 uA. If you look at the data sheet for an LM386 http://www.ti.com/lit/ds/symlink/lm386.pdf p.4 "Quiescent Current", you'll see that for a 12 volt supply the LM386 will draw about 5 mA, or 100 times more than R3. This is with no load on the output.

So the question you need to ask is "How much current can I afford to supply in the off condition?". If the answer is 1 uA, then the following circuit will do you fine. Just be careful about picking Q1 - the attribute you're looking for is Idss with Vg = 0. This varies with model, but I've seen it at 1 uA.

If 1 uA is too much, then I suggest  using your float switch to activate a small relay, and use the contacts of this relay to drive a more powerful relay which will actually drive the pump.







simulate this circuit &ndash; Schematic created using CircuitLab