Basically, depending on your criteria, this design can be fairly simple or fairly complex. Starting simple, you want to know if you have power on a single jack. For that, you can place a LED with a series resistor between the + and -. The resistor value can be calculated from the LED you select. Let's say you have an LED that requires 2.8V@10mA. You can compute the resistor value by the following equation R=(Vsupply-VLed)/CurrentLED. In my example, this would give you a 2k resistor. They can be a bit bright at that value so you can place a higher resistor value (2.7k for example).
If you want 10 LEDs detecting 10 inputs, you can do the previous circuit 10 times. No need for anymore complexity.
Now, if you want to ensure that the voltage is between 22 and 26V, this is a bit more complex. You could do it with transistors and diodes, but, the simplest way to do it is with two comparators. In that approach, your device will require a power source of it's own. So the topology of those 2 comparators is to tie both their in+ together. Connect it to your input signal with a voltage divider (1:10 seems a good ratio). Place you max threshold on the first comparator (with the ratio). You can use a pot to configure the triggering voltage. Then do the same for your low threshold. Finally, place your LED between the output of both comparators with a series resistor. Replicate this circuit for each input (they can share the same Vref). Of course, this circuit is very generic, but without more context, I can't comment any more.
Good luck!