The closest book I have is for a '98 Truck. It appears there IS a single common ground for both headlights. Both lamp grounds go through a "joint connector", but the joint connector has two different ground connections. If the problem is in this area, the wipers, front turn signals and running lights, and high note horn will not work at the same time as when the headlights quit.
Does this problem affect the low and high beams or just the high beams? If both, connect a voltmeter or test light to the 12 gauge Red / White wire on the headlight switch and monitor the voltage when the problem occurs. That's the 12 volt feed wire coming from the 40 amp fuse # 5 under the hood.
If only the high beam is affected, connect the voltmeter to the 16 gauge Light Green / Black wire between the two switches. Knowing what's happening on these wires will help determine were the circuit is opening up under load.
Monday, April 27th, 2009 AT 2:14 PM