I'll try to make this brief: I have noticed some of my lighted switches which stay lit for extended periods heat up from the 2721 indicator bulb. An example of this is the power antenna switch that I added; sometimes I leave it on for hours at a time so I can listen to the radio, and when I turn it off, it feels uncomfortably hot.

I am sure we have all seen switches in a 240 with melted or cracked plastic, and I want to avoid damaging my carefully scrounged switches. Additionally, I have had several 2721 switch bulbs burn out over the years and would like a more durable bulb. My solution? LEDs.

Not wanting to invest a lot money in researching the viability of LED replacements, I found some cheap ones on eBay. Here are two types of LED compared to the original Osram 2721 indicator bulb:



As you can see from above, I found a surface-mount type LED, and a dome type, both claiming to be replacements for the 2721 bulb. Both types of LED cost less than $1 each, even considering shipping. Both types have built-in resistors, and are ready to use with a 12-14v source.

The surface-mount type (see below) was poorly made. The LED was only secured to the plastic wedge-base body with a piece of poorly applied heatshrink tubing. Futher, some of the leads/contacts were cut too long or bent the wrong way. That said, every one of the 10 pieces that I bought lights up bright, fits into the switches, and provides a nice, diffuse light.

I think if the Chinese orphans who assembled these LEDs had used a squirt of epoxy during construction, they would have been very good bulbs. I was able to improve them by cutting away the heatshrink and running some Superglue around the LED.



The dome type LED (below) was too long. On some switches, the colored plastic inserts popped out when I inserted these LEDs, and on others, the super narrow light beam simply left a bright dot on the switch indicator. However, they are better made than the surface mount LEDs.

I was able to solve the length issue and the lack of light diffusion by sanding down the acrylic dome. They now work quite well in all the switches.

As a side note, these dome type LEDs are were perfect as-is for the shift indicator light. PERFECT. They fit without modification and the narrow beam is desired for that purpose.



Below is another comparison showing my modified LEDs and the original 2721 bulb.



After sorting out the fit/quality issues with the LEDs, I wanted to be sure that they actually heated up the switch less than the incandescent bulbs. First, I checked current draw.

The original Osram 2721 bulb drew .13 amps @ 13v.
The surface-mount type LED drew .03 amps @ 13v.
The dome type LED drew bewteen .02 and .03 amps @ 13v (My meter's resolution is only good to the nearest hundredth of an amp; it kept flip-flopping.)

Next, starting with the switch at 82 degrees F each time, I inserted each type of bulb and measured the temperature of the plastic insert after 10 minutes with an infrared thermometer, recording the hottest reading.

The original Osram 2721 bulb heated up the switch to 180 degrees F in 10 minutes.
The surface-mount LED heated up the switch to 106 degrees F in 10 minutes.
The dome type LED heated up the switch to 94 degrees F in 10 minutes.

Encouraging results, no? I'm expecting these LEDs to last at least as long as the incandescent bulbs have, and I am hoping for longer. Either way, the sub-$1 pricetag makes them cheaper to replace, and I know that my switches are now safe from overheating.

Hopefully somebody else will find this useful.

Sean