OK, I have always had trucks with an isolator, mechanical type, so when my trailer is hooked up and plugged in, it's connected as long as I am in the "run" position on my truck.

So when I shut it off, the trailer battery becomes isolated from the truck, so if I leave a trailer light in, it doesn't run the truck battery down.

I didn't realize this till I found my truck batteries dead from my trailer being plugged into it.

I am considering installing a continuous duty solenoid run by the key in the run position.

Has anyone else run into this?

Now that I am aware, I unplug my trailer when I am stopped with the trailer hooked up for a while.