Speaking for 02 mustangs and on, (with the trac, rear defrost, and fog light buttons) they are lighted by a 2mm led which is not soldered. You have to take the buttons out of the center bezel, unplug the harnesses running to each button, pop the top of the button off, and if you want to replace the "green" led, you have to pry apart the button shaft housing while pulling simultaneously (its a beeyoch). There are actually two leds in the button housing, I only replaced the "main" one that lights up when you have your lights on. The new led has to have a resistor on it or it will fry, or you need a led that can handle 12 volts that is 2 mm in size (i think 3 mm leds will fit, but it's tight). You will see how the stock led is connected, I was able to order some 12 Volt blue leds with resistors already soldered to it from ebay. After fuggin up the first 5 leds, I got it to work. My interior looks great now (blue / red) theme. I want to change out the radio, but need someone to post how to on that. I have never soldered anything...