I own a 2000 Xterra SE 4WD. While pulling a 600 lb motorcycle on an average size trailor, my instrumentation lights on my dashboard (they light up the tach, speedo, fuel, and temp), flickered twice then went out. Also the tone sound that you here when you leave your lights on and open the door does not work. Every other electrical device works fine. I've checked all fuses. Any ideas? Thanks for your time.