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Discussion Starter #1
My '99 DeVille with 57,000 miles on it has a headlight problem. The headlights stay on after the vehicle has been turned off. I had to pull the headlight fuse in the fusebox to save the battery from running down.

The twilight slide control is in the off position, and the headlight switch is off also. After the ignition is turned off, the usual delay before the the interior lights shutdown occurs, but the headlights stay on!

Help from anyone is appreciated.
 

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Here is how it is supposed to work!

There is a photo cell in the cabin to altert the computer to the status of available light. The computer in turn determines if the headlamps are required, then powers the relay if needed.

The automatic shut down of electrical systems is controlled by a timer circuit in the BCM and a relay.

Sometimes when the "autolamp" is left turned on, it fails. Also, sometimes when the "autolamp" is turned off for a few days, the problem is resolved after the headlamps are turned on manually during this period. Don't ask me why a few days, but not using the automatic lamps for a few days seems to work.

If this is NOT the problem, because the headlamps come on during the day, and stay on, the photo cell is likely bad.
 

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Discussion Starter #3
Thanks for the reply, However, This morning when I checked the lights...
I had to put the fuse for the headlights back in (I had removed it to save the battery). Now, the lights will not come on! The twilight switch is (and has been) in the off position. The headlight pull switch will illuminate the instument panel when I pull it out but still the headlights will NOT come on. The running lights do come on when the shift lever is in Drive.
Now I am more confused then ever.
Note: I placed a towel over the light sensor in the dash, and the "headlights suggested" indicator displayed on the information panel on the dash.
?????????
 

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jp99caddy said:
Note: I placed a towel over the light sensor in the dash, and the "headlights suggested" indicator displayed on the information panel on the dash.
?????????
That would lead me to believe that the sensor is working as intended.
 

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Discussion Starter #5 (Edited)
I found & fixed the problem. Under the hood over the left wheelwell, along side the fusebox is a series of relays. When I tapped the headlight relay with the back of a screwdriver the lights either went on or off. Obviously the relay was faulty. So, I replaced the relay, and all is well.
Thanks for the help!
 

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This is very helpful... My 99 Deville has just experienced the same issue. I brought it to the dealer and they informed me that 6 relays should be replaced. They want over $300 to replace these relays!! I am very mechanically inclined , so is this a difficult job or can it be done by someone who is handy?

Thanks..
 
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