They're lit from behind. Easy to replace the bulbs. If you want to replace, I'd suggest considering replacing all the interior bulbs with LED while your in there; very easy, inexpensive and a huge improvement. Probably one of the best bang for your buck things you can do.
Yeah, found it. It had gotten pushed back when I put the dash back together. Guess that's not bad if that's the only wire I missed when doing the heater core replacement.