I have a 2017 Subaru Legacy. A month ago U-Haul installed a trailer hitch and electrical kit. I used my 5 by 8 trailer (bought at Tractor Supply) happily for three weeks. Then one day the car did not start when the trailer was connected. We tried disconnecting the trailer's electrical ribbon and voilà, the car started. We moved the ribbon over to where it would get pinched less from the trunk closing on top of it, and then all seemed well.
However, the next day, the problem returned, worse than before. The car would not start with the trailer connected or without. We tried a jump with our other car but that didn't help. We had the car towed to the AAA approved shop in our area, which delayed looking at the car for three days, and then referred us out to the dealer.
The car was then towed to the dealer, arriving mid-afternoon on Friday. The dealer said the arrival was too late in the day for it to be looked at before Monday.
Now they have looked at it, and say that there was a short with the U-haul wiring kit installation, and the battery is fried, because it was fully discharged for too long, and should be replaced.
I read that fully discharging a battery can indeed cause irreversible damage. (1) At what point did the irreversible damage probably occur? (2) If we ever have this problem again, what, if anything, should I do differently?
(3) Should I now install a Subaru wiring harness instead of having U-Haul try to improve things? The Subaru dealer service manager says that after-market parts are not always completely compatible.
If the two types are equivalent, I'll go with U-Haul because I need to be using the trailer. The dealer said the harness needs to be ordered and would likely arrive on Wednesday (in two days).
The most important question in the short term is (3).