They could be on the same circuit. There is a chance that the slipring in the steering column is worn out and isn't making contact any more, so the button on the steering wheel might not be getting any power. Which connectors are getting power? Check for a coin in the cig lighter socket, that is very common with minivans (you think I'm joking..)and will blow a fuse instantly. If the radio is dead, it might be causing the blown fuse also, or it could be that it's not getting power and is only lighting up because of some strange way that the illumination/dimmer circuit is designed in that particular unit. Everything (cig lighter, radio, etc.) can be disconnected, so you can try to eliminate whatever device is blowing fuses. This of course assumes that the problem is with the device and not the wiring harness. It's a place to start though.