Headlights won't turn off, even with the car off.

This afternoon, when my wife went to start my 2001 prius, it was dead. I disconnected the 12V battery (relatively new) and checked the voltage. About 3 volts. So I put a charger on it and hoped. After about 12 hours it seemed to have enough charge to try it, and immediately the headlights turned on. I jumped in the car to turn off the headlights but they wouldn't turn off. I honestly don't know if the switch was in the on position to start with, but it's definitely in the off position now, and the lights are still on.

Anyone have any idea what's going on here?

 

The 12v battery was disconnected for the better part of yesterday when it was recharging. When I reconnected it was when I discovered that the lights came on. I played with the switch, and pulled some fuses and relays under the hood so the headlights no longer come on, but the running lights still come on. I haven't tried disconnecting the switch yet.

I have an idea what might have caused this. The weather had been cold for the past week, with snow on the ground. Two days ago it warmed up, and started raining, and yesterday it was 60 deg with snow on the ground and an intense fog. When I went to drive my truck yesterday the windows were all fogged up, as was the inside rear view mirror, and even the inside of the speedometer. I suspect that the car and truck were both very cold, and stayed cold inside the garage while it got warm outside. Then when it got warm and foggy, the humidity got sucked into all those cold parts of the car and condensed.

I've been running a dehumidifier inside the garage since last night, but the display says it's still 80 percent humidity in there, and a lot of surfaces have moisture on them still.

 

I'm pretty disappointeed in the response to this thread. Usually this forum is pretty active. Maybe I should be more specific:

Does anyone have any idea WHICH COMPONENT could be causing the headlights to come on like this? And where is it located? I tried disconnecting the headlight switch stalk from the steering wheel. No change. I removed a couple of relays and fuses from the fuse box on the drivers side of the engine compartment. Now the headlights don't come on, but the parking lights still do. Also,when I try to start the car, nothing happens.

Right now I've got a hair dryer running inside the car to try to dry it out, but so far... nothing.

 

I'm hesitant to subscribe to the AllData thing because it looks like it would just be a sort of automated version of the toyota manuals, which I have. Under each section it begins "connect OBDII scan tool or hand held tester." Now, maybe if the scan tool has its own power source and can power up the computer to talk to it, that might work, but from what I can see with my scangauge, the computer isn't alive.

Actually though, I had said that the parking lights are on. They aren't. Only the directional lights (all 4) are on. And the only lights on the dashboard are the directional indicator arrows. Both on solid, no flashing.

 

Also, techinfo.toyota.com supports, MS Windows 7, Vista, XP. I have an old Mac.

 

It has been suggested that the lights may be on because the alarm system may think the car has been stolen when the battery died. Any suggestions as to how to tell the car it hasn't been stolen or do I have to take it to Toyota?

 

Ok, I posted the thing about the alarm system this morning quickly, but for anyone that's interested here's some detail about what's been going on. Sometime yesterday I reconnected the battery and nothing came on. Big change, right?

Now remember that I had removed some relays and fuses so the headlights wouldn't come on and drain the battery every time I connected the battery, also I had removed the horn fuse because at some point during this fiasco the horn started sounding. Similar to the way the other lights were on, just the horn sounding continuously. So at that point the only thing that came on whenever the battery was connected was the 4-ways. But now even they didn't come on for some reason.

So I reinstalled the headlight fuses and relays. Still nothing came on. Reinstalled the horn fuse, and it sounds continuously (so that got removed, but the rest stayed in.)

Still there were no lights in the rest of the car. No dash lights, no response to the key, no dome light, no trunk light. So I started checking other fuses and found about 4 blown fuses. I replaced them, and tried to start the car. Nothing. Then, while the key was still sitting in the ignition in the run position, suddenly the car started. I freaked out and shut it off (I was in a closed garage) than tried to restart it. It started fine, but the airbag light was on, along with the ABS and Brake light. I turned it off and started clearing up tools and stuff that was behind the car, and while I was outside of the car I noticed the "door open" light was on. Checked all the doors. They were all closed. Opened the garage door and tried to restart the car. Nothing. Checked the fuses again. They're all good. Tried to start the car again, it gives me the triangle with exclamation mark.

I checked the scangauge for codes, and came up with P0000 and P3002. Tried to start it again. Nothing. Disconnected the scangauge, it starts. Drove it around the block. Brakes feel low, but they work. (brake light is still on).

So at this point I disconnected the battery, so that if something weird happens in the middle of the night it won't kill the battery. I'll reconnect it in the morning and see if it starts. If it does, I'll drive it to toyota and see what they say.

 

Well, it seems the car runs pretty much fine as long as the 12V battery is charged, but the car dies when the battery gets low, and apparently the charging system isn't charging the battery. Which is weird, because I used the scangauge to check the voltage and got 13.6 volts. I would have thought that if the inverter is putting out 13.6 volts into the same power bus that's powering the vehicle that the battery should be getting charged.

I'm looking for the charging system section of the service manuals, but it doesn't seem to be in body electrical.

Anyway, I drove the car to work yesterday (closer to Toyota) and it seemed to work fine, but when I called Toyota, they couldn't take me. So I tried to drive the car home. Made it a couple of miles before the display died, then the car died. I turned off the headlights and made it back to work, where I left it. I have the battery at home, on the charger, but I have to go back and put it in the car to get the car home.

I think it's time to buy a new car, although I really would like to know what is wrong with this one.

 

I did check the battery OCV after the car died yesterday and got about 11.4 volts with a DMM. I don't know what it would have been in ready state, because by that point the electronics wouldn't start up. I left the car at work overnight and brought the battery home to charge it here. I'm assuming that when I bring a fully charged battery back it will run as well as it did yesterday morning.

But yeah, I want to check the voltage at the battery while running. I'm hoping it's as you say, just a bad connection. But I'm afraid with all the weird electrical stuff going on that the charging system itself is compromised.

Where in the car is the 12V DC generated? In the inverter? If it wasn't working properly would that give a diagnostic code?