ThaEdge
Newbie
Strange. My dually has a solenoid and a long wire wrapped around the ABS pump and redundantly connected to something. It was defeated when the passenger battery was deleted. It makes me think GM didn't wire them as simply as has been described so far. I never have seen a schematic that shows this piece either. The solenoid is mounted to the fender back by the power distribution box. I too have had excellent luck with single batteries, but I do remember having less luck with batteries in general back when I lived in upper MI. One thing duals are good for is if the batteries are weak or freeze, you have a little extra to help you fire it off. Or if you have a hard starting POS.
That was a diy addition not factory or dealer add on.