Thanks for all the responses, folks!
I guess we'll live with the steering wheel controls not being lighted. Seems kinda stupid, though (IMHO). There were many other vehicles, in the same model year, with lighted steering wheel controls. Makes one wonder why Nissan didn't see fit to do the same with their vehicle...
Thanks for your input, Rabs13...
I had thought that maybe it had to do with the entertainment system (in my girlfriend's case, the DVD system), but playing the system and switching to AUX mode on the head unit didn't do anything. (I should add: Other than an owner's manual that deals only with the base Pathfinder, she received no other manuals. Not for the NAV system or the entertainment system.) Either the systems are not linked, or it was possibly disconnected for a hands-free cel phone kit. Is this a possibility? There was such a kit in her vehicle when she purchased it, and I have since taken it out. But, other than the power and ground leads, there appeared to be no other connections or splices with the vehicle's wiring. Someday, when I've got a little free time on my hands, I'll have to tear back into the dash to do a little more investigating, and hopefully come up with a way to utilize that AUX switch for her MP3 player.
Thanks for all your help!
