Not totally applicable to EVs. Don't leave your removable towbar on your car for a year. We've been using it periodically over the year, so got lazy in taking it off Inbetween.
So first problem, randomly the car would say the trailer is connected when it wasn't. This appeared after the heavy rains we had.
Awkward investigation once disassembled revealed the recessed trailer socket full of water 💦.
I used an airline to blow out the water. But it kept coming. In the end I had to completely disassemble the socket. It's a two piece part where the wires are on a connector that clips into a cup shape with all the pinouts located. This is where the water was collected and shorting the plug pins. I thoroughly airline dried the assembly. Blathered it in di electric grease, so no water could ingress into the connections from the top or sit in this recessed cup.
Drilled some strategic holes in the casing where water could collect. This should let it drain if it ever gets water again
View attachment 671887
Then after a couple of hours of this, thought it better to remove the towbar- it was seized in place. Liberal doses of WD40 and airline to force it down the locking key slot. Eventually it came lose, so the key would turn.
Hooray. 4 hours of time spent when 2 mins removing towbar would have done fine