I got tired of poor illumination of the gauges on my 77 300d. I bought two T1-3/4 sized white LEDs. Drilled a couple holes at the end of the light pipes (opposite where the light bulbs go). Wired them in with a 1K 1/4 watt resistor in series with each one (1 LED and 1 resistor in series, do this twice, one for each light pipe). Ran to the variable voltage side of the Rheostat. Threw away those incandescents. Now it works excellent.

Remember, you must angle in the LEDs a bit to reflect off the diffuser at the front of the light pipe.

Keith