AIUI, for some time LED replacements for incandescent dashboard bulbs have been available. LEDs may not be as cheap as the old- tech bulbs (I am assuming); but, considering the cost (real-cash or personal-time-virtual) of replacement and the potential price of crudding up some part of the car during the work, surely they amount to no-brainer substitutes, especially in older cars with simpler circuitry (ie, no weird issues with polarity or voltage)?
There appears to be a market for LED replacements, at least for flashlight bulbs. In the case of flashlight LED's, the base of the bulb serves as the adapter that takes care of polarity and voltage. I got an 3-LED replacement for my mini-mag light, and at $7.95, it is almost 8 times the cost of the incandescent bulb but the 3 LED's give a whiter light and the batteries last at least 4 times as long. As a frequent camper and tinkerer, the LED setup paid for itself in about 2 months in batteries alone.
I've noticed that LED's are used much more frequently in tail light and brake light applications. Assuming that they consume less power for a given light output, then the wiring for the lights can be a thinner gauge that weighs less, and with enough reduction in energy use, the alternator can be downsized and made lighter.
Hadn't considered that but it makes sense; such details add up. They are also more robust. (Side note: in the 1960s, the Royal Navy -- in common with most modern navies, I expect -- needed a replacement for the incandescent signal bulbs used in their big ship-board gun batteries: whenever one of those megabeggers let rip, the shock wave would kill bulbs and lead to a mad scramble to swap in fresh ones. They got interested in numerous oddball technologies. The invention of LEDs must have been a relief.)
I do recall seeing a website selling LEDs made for the vehicle- repair trade: ie, with appropriate shapes. AIUI Audi (eg) have fitted wire-in LEDs for dashboard indicators for years. Mostly I wanted to learn whether today's car repairers would routinely consider replacement by LED bulbs.
When Volvo originated the use of LEDs in brake lights, the point the company made was that these start giving useful light faster than incandescents, by a potentially lifesaving number of msec.
Eg: at 60mph, 10msec correspond to 10.56", not likely to help in many accidents maybe, but nice to have. ISTR incandescent brake lights need more than 10msec to reach signal brightness but have no reference handy (being offline).
Google 12v 194 LED
One of the first sites that came up has a direct replacement for the dash-board twist-ins for about $6 each. That's cheaper than OEM, and you can change the color of you guage cluster!
Thanks for chasing this. _Cheaper_ than OEM rather rubs in the salt; last time I checked, the LED bulbs were still pricey(ish).
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