External LED

1.1-a

The power PWR and activity ACTpins are on the board behind the SD Card. You can install 1/8w resistors at R1/R2 on the top edge of the PCB. Kits and Assembled units come with 330ohm, but anything between 300-500 should be safe. Your LED will be dimmer the higher the resistance. You can use the calculator at the bottom to calculate the exact resistance you need if you know the LED value.

1.0-a/b/c

Power

Connect a LED to 5v with a resistor rated for your LED.

Activity

There are a few options, but none would be considered easy.

Use the latest firmware & directly connect to PA0

If you are on the latest firmware you can use the same pin, PA0 as 1.1 does, you will have to solder it yourself.

Remove existing LED

Remove the existing PC13 led and solder on your own, not recommended, but works.

Recommend LED and Resistors

https://www.mouser.com/technical-resources/conversion-calculators/led-series-resistor-calculator