It's a 3 channel dew controller. http://dslrmodifications.com/DewController/DewController.html
The only thing I wanted to do was wire in red LEDs onto each of the circuits so that we knew there was power going to each of the channels. I have some that already have the resistor wired into it. The LEDs work fine on 12V power when I tested them. I also have some 3mm ones.
On each of the three circuits I added an LED and it didn't light up when I plugged in a dew control strip and turned it up. The controller actually works, because I could feel the strip get warmer, but the LEDs wouldn't glow.
I wired the LED with the anode (+) to the center post and the cathode (-) to the side binding post of the RCA jack.
B