I installed a LED to my heater button today. Got a bit fed up at night trying to work out what heater setting I was on. I actually followed this link from 107 Blogspot. http://my107.blogspot.com/2009/06/led-in-heater-button.html I bought a 3mm LEd from eBay. Make sure its a "prewired LED" as it will have a black, and a red cable to tell you the polarity. If you dont buy a pre-wired LED then you`ll just have a LED, and nothing else. I found 3mm was the right size to fit that small round cirle