What causes the headlights to switch on automatically when you put the key on?

fuses check first
and scan the PCm is next, for DTC errors
this HL system is DLR, and work like the users guide tells and has sun sensor. too. and we all know DLR loves to fail
car drives perfectly not told, and matters.

qod:
"What could be causing the relays to buzz and the lights to be on even with the key out of the ignition and the light switch turned to off or automatic"
well if you scan the PCM/BMC obd2 port
and it told you the BCM is failing what then.?
THE BUZZ MAY BE ONE LCM DEVICE IS SHORTED
THE BUZZ IS THE CLUE .
SCAN THE PCM.

key off the BCM must turn off head lamps NO. not fully truth
elaborating?
The head lamps work key on, key off , and running or sun sensor says dark.
key off and HL switch of sure the HL must turn off or the BCM is bad or the switch telling it OFF is bad.
Key if lamps must work on demand, if not bcm bad or cars battery is dead, /weak, I asked if engine runs and fuses all tested good, front bay and cab fuse boxes.
FSM factory service manual words now. reading to you now.
on this car the HL switch 7 pos. wire to the LCM
lighting control module
2 fuses, 2.7 and f2.31 must be good. in the CJB
the central JUNCTION BOX. (FUSE BOX LINGO)
LCM HAS 8 FUSES. WOW.
LCM RUNS HIGH BEAMS LEFT AND RIGHT,,
NOT MARRIED, TO 1 WIRE.
THE LCM DRIVES THE WIPER WASHER DIRECTLY
THE LCM DRIVE POWER TO PIN2 ON WIPER MOTOR
SO PULL THE WIPER MOTOR CONNECTOR AT MOTOR
SEE IF BUZZ STOPS
LCM IS REALLY A BCM BUT THEY CALLED IT WRONG
BUT CAR IS OLD AND THEY DID THAT.
LCM RUNS VAST THINGS ON THIS CAR.
EVAN THEFT SWITCH AND HOOD AJAR SWITCH
NOT SCANNING THE PCM PORT YOU MISS ALL THOSE FAILURES. CODES
IS THE PATS LAMP HAPPY, IMMOBILIZER?
BE A SHAME IF HOOD SWITCH BAD
AND LIGHTS FAIL, HOOD UP MEANS WORKING UNDER HOOD, DAY OR NIGHT AND WHAT THAT DOES AT NIGHT IDK. BUT

FUSES ALL GOOD TESTED SO
SCAN THE PCM./BCM PORT, OBD2, TOOLS WORKS
LCM PAGE1 OF MANY.
https://imgur.com/a/Ih5l2Jd

There could be several potential causes for both the tail lights and headlights not working and for the headlights turning on the brights when the vehicle is placed in gear. Some possible causes include:

1. A blown fuse: If a fuse has blown, it can cause the lights to stop working. Check the fuse box and replace any blown fuses.
2. A problem with the wiring: If the wiring has become damaged or has come loose, it could cause issues with the lights.
3. A malfunctioning light switch: The light switch might not be functioning properly, which could cause the lights to not work.
4. A problem with the headlight switch: If the headlight switch is malfunctioning, it could cause the headlights to turn on the brights when the vehicle is placed in gear.
5. A problem with the dimmer switch: If the dimmer switch is not functioning properly, it could cause the headlights to turn on the brights when the vehicle is placed in gear.

It's recommended to have a mechanic diagnose the issue to determine the cause and recommend the necessary repairs.

I will fill in the blanks....you must have a newer car with auto head lights....there is a setting on the headlight switch that lets you over ride the "automatic" headlight mode....maybe you or someone accidently turned it to the manual "on" position...if so turn it back to the "auto" setting......2nd....new cars do have a delay before the headlights go out after parking your car. And if you read your manual, you would see that the time they stay on after turning your ignition key off can be set to several different time settings, including to switch off as soon as you turn the key off.
But if you had accidently turned the light switch to the "on" setting.... fear not....the headlights will automatically go off after the battery is dead....lol....actually they should go off within 2-3 minutes of turning the key off...unless you have an open door or trunk...or engine hood...or maybe even a gas cap door...and your car is telling you "something's open" by the lights staying on....Take that Jim and see if it gets you anywhere.

Normally this condition is the result of a poor body ground connection. Testing for this can be deceiving. At the static(nothing on) condition, testing can show a good ground. However when a circuit is excited, it has a determined resistance and a set current flow. If the ground connection to this or a branch circuit is loose, corroded, or broken wire. This will allow just enough connection to show as being good, but not good enough to complete the circuit with the required amount of connection when energized.

Could be the ignition switch itself. Under the hood where all the wires go into the fusebox in the cab is a good pkace to start. You need to take the bolt/nut off and pull the box and wires apart. I have seen fuse blocks heavily corroded and cause problems as you are haveing. Also could be the ecm (aka)computer in your car is going bad. You can get a remanufactured one cheap. And it is simple and strait forward

this is caused by you delay switch or relay staying in the closed position causing it to short out . or if your headlight switch is on the steering colume and acts as a signal light switch used for low and high beam will need replacing

A short circuit,auto diagnostic tool.

IF automatic transmission, put the key in the run position. Turn on the headlights, put the transmission in reverse, apply parking brake, get out, go to the rear of the vehicle. IF the rear back up lights are NOT on, you need a new neutral safety switch, and possibly a new wiring harness for this switch.
The switch should be located on the driver's side of the transmission, above the pan seal, near the rear of the pan. 1 inch deep well socket to remove and replace - will spill transmission fluid, have more Mercon-Dextron III available to replace what you loose.
If this fixes your problem, you should probably change the transmission fluid and filter - dirty fluid probably caused the failure in the first place.
Hope this helps...

Sounds like your light sensor is messed up. The sensor that controls everything on automatic mode. Good luck.

OMG! Isn't there a headlight switch in that car? i dont think they come on automatically at night..