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(PWR)/R2(ACT) 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 of this page 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 which require soldering.
Use the latest firmware & connect to Pin A0
If you are on the latest firmware you can use the same pin, A0 as 1.1 does, you will have to solder it yourself. Remember to add an appropriate resistor between 300-500ohms.
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
