I recently built a test led for caliubrating the AMM CO setting. I have a tip for those looking to build one. Radio shack sells a twelve volt LED w/ a built in resistor for 99 cents. This will eliminate the need to buy both an LED and a resistor. I used a small piece of copper clad board and some echant and made a little circuit board to solder the LED to. Just two pads to solder the LED leads and a + trace leading to a large sqare pad and a trace leading to a large - pad. I made separate leads with alligator clips and spade connectors and just clip the leads to the + and minus pads on the board when testing. no need to make your own circuit board, but I just happened to have the supplies on hand. A bottle of echant is $4 at radio shack, and a piece of copper clad circiut board is just a couple of bucks if you want to do it up nice. You can use a Sharpie magic marker to draw the traces. It beats paying $40 for one premade.