The LED is an automotive LED with a built in resistor. I soldered extra wires and added the alligator clips. This has been my go-to tool for a lot of the activation signal tests I perform!
The LED is polarity specific. This means that voltage will only pass from the LED's red lead to its black lead. This also means that you have to pay close attention to the testing instructions so that your connections are correct.
Do not substitute a regular 12 Volt automotive test light where ever a TEST calls for an LED light!
I used to buy my LEDs from Radio Shack, but of course they no longer sell them. You can try Fry's Electronics (if you have one in your locality). Or you can buy one from me:
1 LED Panel Light
2 LED Panel Lights