5V Power Test Pen

Hardware:

1x 3mm LED
1x ¼ watt resistor (330 ohm to 2k ohm) 
1x breadboard jumper wire cut in half (female side)

I printed this with a 0.4mm nozzle, but 0.2mm should work too.

Assemble the two halves with pins, and glue on the tip.

I soldered together the parts, but they can easily be twisted in place too.