hope this helps a bit...
hmm, yeah, that stupid twilight sentennial. I wish I just had DRL'* (for foggy days when I want lights and they don't turn on, and I don't turn 'em on cause I'm too lazy to pull that damn thing out). Anyhow, I would guess it'* the switch. The unit on your dash that monitors the light level is a really solid component, and rarely goes bad (less than 1 in ten thousand perhaps), and if it did, would more than likely have already been diagnosed and replaced at the factory.
so, the circuitry would be my second thing to check; first being the switch. switches go bad, it'* a fact. Moving parts go bad long before solid state components (the electronics controlling your lighting), so for that fact a lone, I would go to a junk yard, find another switch, and replace the one in your car. It'* prolly the easiest thing to try.
It'd be a good idea to check all of your fuses. That particualar system doesn't have a fuse of it'* own, but I always check the fuses first when something happens.
I guess, going back to the whole switch deal, once you pull it out to work on it, if you feel comfortable doing so, you could short the right wires (just two of them) to simulate the switch being on. that would tell you if it'* bad or not.
'95 SSEi, few electronic mods (and a stupid coupler)
HU (Sony MDX-CA680, European Ver; Sony 4x3-ways; 91, 93dB)
Yup, that'* ISU