BG

I found a link to a circuit that is identical to what you want, but the voltage of the battery is not the same. The circuit is based on using op amps as comparators, and is quite simple. This circuit should work just fine for you, but you will likely need to change some of the resistor values and the reference voltage to get it to work at 36 volts. You might just be able to use a different reference voltage depending on what voltages the lights need to go on at. A comparator works by comparing two voltages, one is your reference voltage and the other is the one you are measuring. In this circuit you want something to happen at 3 distinct voltages, so you need 3 reference voltages, these are obtained by using resistors to divide the reference voltage. The circuit is really like 3 separate circuits for each voltage measurement. Play around with this circuit on a bread board with some potentiometers for the resistors, its quite simple, and if you don't know electronics its a good one to experiment with.