surveyranger:
Looks like a Nano should be able to supply up to 500mA on the 5V supply so 59mA shouldn't be a problem.
Wrong.
The 5volt regulator of a Nano has almost no heatsink.
Anything more than 0.5watt will result in an overheating regulator.
If you drop 12-5 = 7volt, then that's a max current of 0.5watt/7volt = ~70mA.
If you subtract ~30mA from that for the Nano itself, then you have ~40mA max left for the pot/LED/relay.
A common relay module with optocoupler draws 2mA from the output pin, and about 75mA from the 5volt pin.
So there's your problem. You basically can't/shouldn't power a Nano from 12volt.
Use a 5volt buck converter, and power the Nano and relay module from that.
Leo..