I have a 2000 Isuzu Rodeo with cruise control installed at the dealership when I bought it. It has worked fine, until recently. It works when the headlights are not on, but at night when I need the headlights, the cruise control cuts off as soon as I turn the lights on. What could be my problem?

Optional Information:
2000 Isuzu

Already Tried:
i have checked fuses