The in-dash light depends on which model year you have. If it's 98 & maybe 99 then you may not even have the bulb in the dash. Otherwise it's something the dealer programs in the AAM. Note:Lots of people find the dash light annoying as it's qute bright, besides if you cannot see that the fogs are on then they probably aren't doing you any good anyway.

I'm pretty sure the light in the taillight is always enabled and when you press the dash switch up and then walk to the back to look at your taillight cluster i'm sure you'll see the single foglight on.

The front foglight wiring is set to only allow one set of fogs on at a time. So if it controls the brush guard set then the set in the headlights will not turn on and vice versa. You could have the dealer turn on the internal light then add a seperate switch and wiring for the brushguard set to enable all 3 to be on at once. OF course it's illegal to have all 3 lit up on public roads. By the way, the headlamp foglight is only on the older ML not the facelifted bug eye one. The revised ML has fogs in the bumper.