This is a very simple but useful LED tester that lets you test, compare and check the colour of just about any two pin LED.
To make it you will need the following:-
A PP3 battery connector. A 470 ohm resistor. A bit of heat-shrink sleeving to cover the resistor. A two pin Molex style 0.1" (2.54mm) pitch miniature socket. Two contacts for the socket. A PP3 9V battery. Alkaline preferred.