I usually leave mine hooked up overnight. I have never ran into a problem in 15 years of doing so. That way, I don't forget to plug it in during some of my early-morning departures.
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John W. Irwin
2018 Interstate GT, "Sabre-Dog V"
WBCCI #9632
If your Expedition is anything like the bigger Ford trucks, there's a relay that connects the truck alternator and battery to the trailer 12V circuit when the ignition key is in the "Run" position, and disconnects it when it's in any other position, including Off with the key removed. This keeps the trailer from draining the truck battery (and also keeps the converter from charging the truck battery).
My 2000 GMC 3500 had dual batteries, and the relay that Moe speaks of. It kept the aux battery connected to the trailer at all times, but isolated the main battery from the trailer. Not sure how the diesel is as I believe it uses both batteries for starting. I'll have to throw a VM on that pin of the rear connector and find out.
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ARS WA8ZYT
2003 GMC 2500HD 4X4 D/A Ext. Cab
Propane Powered Honda EU2000i
Lots of Hot Sauce! Air # 283
WBCCI 1350
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