This is not a problem. If you are on auto-headlights (and ONLY on auto-headlights), the headlights will turn on when you'll turn on the wipers and when you turn them off, the headlights come off. On the Journey, each time the headlights turns off, the instrument panel dim. This is just normal (kind of feature of the car)!
If it does not dim, it is because you are not on auto-headlights or because you didn't use the wipers long enough to make the headlights turn on (takes maybe 1 minute).