Just the bulb gets replaced separately, but do so in pairs.
The Sylvania ultra bright are rally nice (silver star or something
like that- I don't remember the exact name). Just avoid any that say
"ultra blue" or similar names.
The switches have a separate light bulb in them for illumination I
think... At least the older switches did AFAIK.. which often is not
much...

            __  __
    Randy & \ \/ /alerie's
             \__/olvos
'90 245 Estate  -  '93 965 Estate
  "Shelby"     &      "Kate"

Open the hood, look at the back of the headlamp, twist the lock-ring and the
connector/bulb will pull out... I just use Volvo OEM lamps... they aren't
any more expensive then a good quality halogen from any other brand... And
they last a long time (Silverstars don't last long, but they have better
light output, I had some in my Golf for about a year, went thru 3 sets of
them... luckily Canadian Tire took back the burnt out bulbs and gave me my
money back each time).

Check the fuses for the seat heaters... If not, probably a harness somewhere
that is disconnected.