See post 957. On-off-on switch with a feed from the out to one 'on' and a feed from the in to the other 'on'.
It would be as cheap to buy the built in led pretty much anyway DC-DC 4.5-28V to 1.3V-25V Power Supply Module LM2596 With Red LED Voltmeter | eBay
It would be as cheap to buy the built in led pretty much anyway DC-DC 4.5-28V to 1.3V-25V Power Supply Module LM2596 With Red LED Voltmeter | eBay