A frequent complaint from the owners of older Porsches is that the instrument lights are not bright enough. In most cases, the instrument light bulbs are the original factory ones, and over the years, they have lost their brightness. Often, the only thing that is needed to make the lights brighter is to replace these old bulbs with new ones, a procedure that can be done in just a few minutes' time. For a 911SC, you will need a total of eight 12 volt, 2 watt bulbs-"indicator lamps", as they are termed by Osram, one of the manufacturers.
To begin, pull the instrument from the dash. In the early cars, before the early 70s, this takes a bit more work, because the instruments are held in the dash with a U-shaped bracket, which must be unfastened from the luggage boot. On the 911SCs and later, only the rubber collar around each one holds the instruments, and they can be pulled or pried out from the driver's seat. If an instrument is stubborn, I use a stiff putty knife to pry it out, with a piece of wood (paint stir stick works well) to protect the dash from dings. Once you have an instrument out, you can reach behind the others and easily push them out.
It is not necessary or desirable to completely remove or disconnect each instrument. Just pull it out far enough to access the light bulb holders. The fuel/oil tank combination gauge and clock have one light bulb each, and the other three gauges have two light bulbs each. Use a tiny screwdriver to pry the bulbholders from the instrument-don't pull on the wire. The bulbs are bayonet mount, so just push in slightly and rotate the bulb to remove it from the holder. Replace the bulbs with new 12 volt, 2 watt bulbs, put the instruments back in the dash, and enjoy gauges that are much more readable at night.