I don't understand electricity. Help me understand my headlights

I don't understand this headlight behavior in my XJ. Nothing broken, but I don't understand how this works and I want to learn.

Driving with my headlights on. Turn car off. Set lightswitch to off. Lights stay on. Turn car back on. Lights turn off.

or

Key not in ignition. Set lightswitch to on. Lights come on. Set lightswitch to off. Lights stay on. Turn key on. Lights go off.

So it only will turn the lights off when the key is on, but it will turn the lights on when the key is off. Some sort of latching relay? Some backfed voltage? Something else completely?

Programmed to stay on for a period of time so the hooligans can't get you on the walk to the house?

Ok, so I dont know how your specific headlights are wired, but it's an xj, so I'm gonna assume its fairly simple. Head switch energizes a relay, the relay supplies power to the headlights. It sounds like the relay is sticking on for some reason. Possibly a faulty relay, possibly some sort of back feed. The first thing to do is check the relay. Mfg's typically use a bunch of the same relay, so find your headlight relay, and swap it out with another relay of the same part number. I usually use the horn relay. If the problem goes away, it was a bad relay. If not, you have a deeper electrical issue. Now you need a wiring diagram and dvom or at least a test light. Or just throw a credit card at it if you dont speak electron.

Edit; if the behavior your describing is reliable and consistent I doubt the relay is the problem. I like troubleshooting this kind of stuff. If you get a diagram I will try to help more.

Is this behavior new or has this always been how the headlights act?

Relay or stray voltage, I suspect. Do the relay swap gearheadmb suggested first, then break out the multimeter and wiring diagram and start checking for voltage or ground on the wires going into the relay.

Streetwiseguy said:

Programmed to stay on for a period of time so the hooligans can't get you on the walk to the house?

That's what the behavior sounds like to me. The headlight delay feature would behave the way you describe.

If you turn the headlights off after you turn off the engine, do they turn off after a period of time? Or after locking the vehicle?

If you haven't tried, wait to see if the lights will turn off after a couple minutes when you turn them off after the ignition. Some of those systems could take several minutes to shut the headlights off. 

Situation 1 is normal for an XJ. It's a 30 sec headlight delay if you turn the ignition off first. If you turn the lights off before the ignition, they should just stay off.

I don't know know about situation 2, haven't encountered that. Could be a setting, or a relay going bad.

If I'm interpreting the original post correctly it's not that the system is acting up it's that buzzboy would like to understand how it works.

The short answer is that it's likely using a time delay relay similar to this one -> Link to Generic Time Delay Relay.

The Jeep headlight delay system is annoying and was present on my 1990 XJ and 2000 WJ. The order in which you shut off the car and the lights matter.  Invariably, you will make the incorrect choice for what you want to do.

The good news is that in the case of that XJ, it was a standalone module you could unplug with no other side effects. 

Keith Tanner said:

The Jeep headlight delay system is annoying and was present on my 1990 XJ and 2000 WJ. The order in which you shut off the car and the lights matter.  Invariably, you will make the incorrect choice for what you want to do.

The good news is that in the case of that XJ, it was a standalone module you could unplug with no other side effects. 

Hmm.  I think we need more details.  Like, is this a Jeep or a Jag XJ?  Either way it's probably some weird proprietary system but is it cheap American weird or Expensive British weird. I think we also need some clarity on exactly what question(s) are being asked.

My question was answered but not the answer that I expected. I didn't realize that the XJs have a headlight timer. I also didn't know that delay relays were a thing. I always figured something like on modern Chevys was computerized. Thanks for the help guys. I'd never actually let the lights turn themselves off to know that they would.

Holy timely post.  I replaced the headlights in the wife's new XJ last night and got the stuck on headlight behavior at one point.  Restarting the car turned them back off.  I puzzled about it for a minute, shuddered at what terrible slow death was lurking in a 20 year old Chrysler electrical system and then stop caring.  Glad to know it's actually working as intended.  

Since the XJ experts are here, why do all the power windows only work from the driver's switches, regardless of the lockout button state?  Broken window lockout switch, broken wire in a door jamb?  

GhiaMonster said:

Since the XJ experts are here, why do all the power windows only work from the driver's switches, regardless of the lockout button state?  Broken window lockout switch, broken wire in a door jamb?  

I'm trying to figure this out myself. If I do, I'll report back

GhiaMonster said:

Since the XJ experts are here, why do all the power windows only work from the driver's switches, regardless of the lockout button state?  Broken window lockout switch, broken wire in a door jamb?  

Yes.

I have much success fixing odd electrical issues by checking the ground/earth connections carefully. I suggest check relays and nodules first though.

I was working at a grocery store as a bagger when delayed off headlights started to become more common. I figured it out after helpfully telling multiple customers who just entered the store that they left their lights on. They were all good natured about it.

Power close trunks also took some getting used to.