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I replaced my head light switch, GM NOS and replaced all the dash bulbs while it was apart.
They all dim now and are bright enough for driving at night.
Kinda wish the vac portion of the switch sealed up better.
I wouldn't want them too bright as you will get too much reflection off your eye glasses for you over 50 owners.
Marshal
Virtually every bulb in a C3's interior (and exterior) can be replaced with something brighter (exceptions are the 77-82 bulb that shines down to illuminate the heater controls, and the 'in-line bulb that is in the upper courtesy light).
You can research this by googling the number of the original bulb number and finding out the style base. You can (usually) install anything with this base style into the socket as a replacement. Look at wattages listed for your original bulbs and pick out a bulb with the original base style that has approx. 50% more wattage (or a little less if there are many in the same circuit) and have similar glass bulb dimensions.
You can put higher wattage bulbs in for the stock bulbs...but they will draw more current and put more [electrical] stress on the wiring/fuses.
You could substitute LED's for the incandescents, but most of the LED bulbs have metal housings that don't fit well in the stock GM sockets. And, you will need to install a PWM power module so that the LED bulbs will dim.
IMO, you just need to replace the bulbs with stock 1895 bulbs and clean the grounding connections for the dash lights.