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.
And some LEDs to play with.
Step 1: The battery connector.
The main part of this instructable is a cheap and common PP3 battery connector used to connect to the small rectangular 9V batteries.