Slate CM wrote:
I did some work on a late model Ford, no more than 2 years old, super duty and the 7 pin had 12V all the time. My 2008 Tundra only has power with the key on.
I don't know what "late" model means.. Ford has made changes over the years.. 1980s and before, there was no charge line from factory..
Sometime in the 1990's Ford added a 7 pin connector WITH the charge line ON A RELAY on most any truck with a towing package (IE class 4/5 hitch).
Now with 1990's F150s they often do not put the charge line fuse or relay in, instead it is included in a plastic bag in the glove box.. The owner just needed to put those in..
Vehicles which did not have a towing package often did not have any wiring and the owner had to DIY or pay a mechanic to wire it up.. Often times in those cases nobody ever thought to use a relay so the charge line was often hot always or never connected..
My Dads 1980 F350 never had factory wiring, he installed the wiring himself.. Yeah, he got stranded ONCE with his 5vr in the winter when his furnace ran down the trailer battery AND his truck battery overnight..
After that he always disconnected the trailer when stopping overnight..