For some reason, the switch illumination on the seat heaters is always on (unlike the other switches which are illuminated only when the headlights are on). That's probably why the little bulbs inside tend to burn out more frequently on these switches. Here are steps for replacing the bulb, rather than the whole switch:
- Remove switch from dash by carefully prying out with a screwdriver on the top and bottom edges alternately. As you pry, the harness on the back of the switch may come loose. If not, just disconnect it once the switch is out. Gently prying off the switch cover, then GENTLY using a pair of needle nose pliers works great. There is not a lot of slack in the wiring harness. Brute force is strongly discouraged.
- You will see an outer plastic housing that covers the circuit board, red plastic housing, and rotary dial. This housing can be pried off by inserting thin screwdriver blades under the sides of the switch (should see little prongs sticking into the sides of the housing that have to be pried free). Pull out the housing SLIGHTLY, then lift out the two metal bars at the top and bottom of the switch that act as the catches to hold the switch in the dash. Hold the switch so the side of the dial faces up (circuit board is down), then slide the housing off.
- WARNING - BE VERY CAREFUL OF THE ROTARY DIAL. DON'T DISPLACE IT OFF THE RED PLASTIC HOUSING! There is a microscopic (almost) steel ball that acts as the switch detent; if you lift the dial off the red plastic you'll lose it and never find it.
- Now, the red plastic/dial unit has to be pried vertically up away from the circuit board. You might be able to pry the legs of the red plastic out of the locating holes in the circuit board, but in my case they broke off (no major problem; the outer black plastic housing will hold everything in place on reassembly). You can also just cut or grind the tabs off of the legs on the other side of the circuit board to avoid the chance of breaking the board.
- With the red plastic/dial assembly out of the way, you can unsolder the old bulb and solder in a new one. I recommend the Radio Shack 12V DC, 60mA micro lamps in a 2-pack (Cat. No. 2721092B).
- You can check for functionality by hooking a 12v power source across terminals 3 and 5 (see back of switch); bulb should light. MAKE SURE OF CONTACTS if you do this; this is how an anonymous lister fouled up and blew the rheostat. Pin outs: pin 3 = +12v to light bulb, pin 5 = gnd for bulb, pin 6 = +12v to rheostat, pins 2 and 4 are outputs to control unit. Light bulb function is NOT an indication of switch/circuit functionality.
- Reassembly is a reversal of removal. Don't forget the little black spring clips. After the switch is all back together, when you try to reinstall it, you'll find there's no way to hold the harness in place to force the switch contacts into the harness. One option is to remove the radio, then hold the back of the harness in place with the short end of an Allen wrench while pushing the switch into place. Alternatively, you can remove an adjacent switch.
