Well, great news. I've finally finished (after about 4 months) converting the interior lights of my C70 over to red LEDs. I've enclosed a complete write up as well as a picture... there are MANY more pictures in the technical gallery. Please feel free to ask questions. The write up below is more of a general overview without getting into the nitty gritty... it's a good heads up for some of the issues ANY car owner might face if undertaking a conversion like this. I'm going to post this over in RWD and aftermarket forums as well, sorry for taking up extra space.

-Jon

Conversion of incandescent interior lights to LEDs

For the last few months, I’ve been going through the process of converting the interior lights of my ’99 C70 coupe over to red LEDs. As I’ve been talking about this process on the brickboard and with friends, many people have asked me about some of the problems I’ve run into and about how it went in general. I decided to do a write up on everything I went though, starting with a primer on some of the differences between LEDs and incandescent lights, then covering how those differences affected my conversion.

First of all, LEDs usually operate in the 1.7 to 3.5 volt range (depending on color, make sure you check first!), and the incandescent bulbs in my Volvo run on a full 12 volts. They also draw substantially less amperage, so you can run several LEDs off of a circuit that was used for only one incandescent bulb. Next to consider is that incandescent bulbs illuminate in a 180-degree range. In other words, if you look at a bulb from the top, it puts out just as much light as it does out to the sides. LEDs don’t work that way… they illuminate in a cone shaped pattern that varies in width from 10 to 75 degrees. Usually, the wide angle LEDs are not as bright as the narrow high intensity ones. There are a few other specs for LEDs that you must look at when you decide which ones to use. Luminous intensity, which is measured in millicads (mcd), shows how bright an LED is. Also, the actual color of an LED is indicated by its wavelength, measured in nanometers (nm). Make sure that you have the same wavelength for all of your different LEDs. There are many different shapes of LEDs like oval, cylindrical, square, and rectangular. The lenses are clear or colored, transparent or diffused. The LED shape and lens type usually correspond to the viewing angle. Certain “surface mount” LEDs have wide viewing angles and are fairly bright, but they are EXTREMELY small and difficult to mount. Finally, there are “direct replacement” LEDs that are designed to replace incandescent bulbs. They may have a built in resistor so that they can operate at 12 volts, and some even have the proper mounting base (like a flange or screw base) that allows them to “plug and play” in place of incandescents.

The easiest bulbs to replace were the ones in a “direct lighting” situation, where the LED faces directly at the item being illuminated or there is Lucite light piping to direct the light properly. The switches for the foglights, sunroof, windows, door locks, courtesy lamps, headlights, and seat heaters all had incandescent bulbs that mounted into plastic twist-in bases. These were the easiest to replace; I just had to unwrap the leads of the lamps to free them from the bases and replace them with 12 volt T-1 (3mm) LEDs. In a couple cases, I had to bend the LED 90 degrees to point at the back of the switch you’re illuminating (remember what I said above about viewing angle… some of the bulbs were mounted perpendicular to the switch). In the radio, the LEDs were soldered to the circuit board but Lucite directed the light to the back of the faceplate. They were easy to desolder and replace with the same kind of 12 volt T-1 LEDs (once I dissected the radio, that is). I had to angle the LEDs that illuminated the radio display so that there were no bright and dim spots, but it was relatively simple.

The items that were harder to convert were the climate control and the instrument cluster. The faceplates of those items were not directly lit by light bulbs, but were illuminated more indirectly using backlighting through the sides of the bulbs. Had I just swapped them out for LEDs, there would have been very bright and very dim spots. I had to use several more LEDs (a couple hundred) than there originally were light bulbs (seven!) to get the light distributed evenly. For the instrument cluster, I literally used hundreds of LEDs mounted to a blank breadboard and packed them in as close together as possible to ensure even light distribution. I also used a dremel to sand down the tops of the LEDs to try to diffuse the light (they were transparent) more evenly.

In situations where more than one LED is used to replace a light bulb, you can join them together in parallel and run them off of the connection for one light bulb. I also used lots of 2 volt LEDs and joined them together in series in groups of 6 (2 volts X 6 LEDs = 12 volts draw) so that I didn’t need an in line resistor. Also keep in mind that some of the lights (such as the ones in the door and window switches) are already LEDs. Some of those look different (i.e. the anode and the cathode are reversed) and may already have a built in resistor so check that stuff with a multimeter to avoid messing something up.

In summary, it was a LOT of work and entailed many obstacles I didn’t anticipate. I ended up using about fifty of the 12 volt, T-1 LEDs for the switches and the radio and some of the climate control. I used about a dozen surface mount LEDs soldered in series to small wires to illuminate the rest of the climate control. Finally, I used almost 350 super bright LEDs wired together and mounted on breadboard to directly backlight the instrument panel, odometer, and trip computer. I got all my LEDs from eled.com. Great selection, quick shipping, and good prices for bulk discount. It was worth it and a learned a lot during the process, but make sure you do your homework before you get into it! I was able to finish the job as a result of sheer stubbornness more than anything else. You can see from the pictures some of what I went through and ask any questions you’d like about the specific details of my conversion, just email me at jon_Belmont@yahoo.com
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CPT Jonathan T. Belmont-- '99 C70R 46K 'Valdemar'