LED lights if two or more switches are on at same time
You could do something like this:



simulate this circuit &ndash; Schematic created using CircuitLab
R9 + R10 is 7.07K, which is optimized to maximize the difference between Vcc/2 and the voltage with one switch and two swiches (about 1V nominal difference in each case). 1% resistors are suitable and cost about the same as 5% these days.
Here are the voltages at the comparator vs. the number of switches closed (&gt;6V turns the LED on):