He didn't say, explicitly, as far as I could see. But it was bloody cold where he was, you could see the snow on the surrounding hills. I'd have thought he'd have been frozen by morning if it didn't stay on, and that's something he might have mentioned.
I'm going to give it a shot when the weather is better, just with the car on my drive here, and see what happens. The side-lights are another issue, I think they stay on. Not that they'll draw much power, but if you're trying to be inconspicuous you'd have to cover them up.