Ford has several charging systems and so far is the only manufacturer who puts disconnecting relay on trailer charging wire.
Early Powerstrokes with7.3 engine would not start charging till couple of minutes after engine start. That was due charging voltage killing glow plugs, so instead of making better GP, they solved it by running the engine on battery power till GP would be no longer needed.
That was pretty annoying for me, when I had my truck sitting for months and occasional engine starting was actually killing the batteries, instead of charging them.
Newer trucks have it improved. but each designated aux battery charging on diesel will have delay timer.
