First thing I'd do is check all of your fuses, but after that you might be on the right track with the BCM. My car had a bad BCM (also a 98 GT lol) and none of my interior lights worked. Dash lights worked (for the gauges), but glove box light, map lights, rear lights, floor lights, none of them worked. My power locks, trunk release button and a few other interior things were dead.