I know, but the OP specified a preference for 5V and it's workable for his wire gauge and length so I worked within those parameters. Small switch mode 5V supplies are even more abundant than 12V supplies now. They're called old cell phone chargers.

Ha, I must confess that when a topic is as basic as this,.. the first assumption that I make is that OP has only a concept and it's up to me to give him or her the most practical solution. Also, it's doubtful that among all the parishioners of his church there is no one that has a spare 12V wallwart laying around. Besides that, ... Fatboy could have just as well said that he wants to use a 1.5V cell. I would have ignored that too!

<SNIP> I want to build a "switch indicator box"......
For power, I would like to use a 120vac to 5vdc converter, if possible.<SNIP>

 

There are many ways to do this...

- As recommended, use different resistors to send a variable voltage up the cable and use comparators or an LM3914 on the far end.
- Send a varying current up the cable (this would be better since the voltage drop won't be as much of an issue)
- Use a low voltage AC source, and use diodes in series with the switches and LEDs to control 2 LEDs with each wire (that would let you control up to 4 LEDs with 2 wires and a ground, but you may have issues with hum getting into your sound system if the wire is part of a snake
- Send 2-bit parallel data up the cable, and use a demux or some gates to drive the LEDs.
- Send a serial data stream (RS485?) up the cable

/mike