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Hey everyone gotta question for ya, my buddy stopped the other day with his truck(2005 f350 lariat 6.0 auto) and told me when he was cleaning his bat terminals there was a wire unplugged with nothing around to plug it back into. It's along pass fender between vacuum pump and the battery. I looked on my 05 Ex and have the same plug but mine has a jumper plugged into it. Question is what is this plug for and will it hurt anything to be open or should I try make a jumper like my Ex has?
What you describe, is the connector that would plug into a harness for the secondary alternator on a factory dual alternator equipped truck, and a jumper on non dual alternator trucks such as your Excursion.
That would be the light green with red stripe wire that cancels out the battery indicator warning light on the instrument cluster the moment the vehicle is started and charging system function is detected, from what I'm reading on the wiring diagram, it SHOULD still be charging without the jumper installed, but likely illuminating the battery warning indicator falsely.