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Shine Light on Auto Headlights prob?

Old 09-30-2016, 07:13 AM
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Default Shine Light on Auto Headlights prob?

97 grand here, my headlight switch has the Auto position to the left of OFF. This is known as the DUSK TO DAWN setting. It is blocked over with tape from the original owner.
When I turn it to this spot the headlights will remain on after I shut the car off. Also the lights do not come on at night. My security LED on the dash *does* appear to have the requisite optical sensor for the auto headlights.
Any input from someone who has worked the system would be appreciated.

Last edited by 97grand4.0; 09-30-2016 at 08:01 AM.
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Old 10-01-2016, 09:31 AM
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I work in sensor technology but have not had the pleasure of servicing the auto headlamp system in my WJ. From what you described, it would seem that the sensor itself has a stuck output sending a signal (to a relay?) as though it was always sensing darkness. Else, there may be a stuck relay at-play in here. The sensor may have been damaged (either it was struck or saturated while washing interior window glass). You can test the system function by disconnecting the sensor harness. There should be three wires associated with the function. With the "auto" position turned on, and using a low value resistor (18 to 33 ohms), momentarily connect the resistor at the relay-side connector of the circuit from sensor output line to return (signal pull-down) to see if it triggers the lamps on. If that doesn't work then try your resistor from sensor line to supply side (signal pull-up). Else you could test sensor for change in resistance when exposed to light vs. darkness. If not the sensor then it must be the relay (still assuming there is one).
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Old 10-01-2016, 09:33 AM
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It could be that the headlight switch was replaced with an autolamp style when it could be just the wrong headlight switch
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Old 10-01-2016, 09:47 AM
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X2 what Willy55 said. It could be that as-well...

Upon reviewing schematics I believe I have misinformed you. Please disregard most or all of my theorizing and troubleshooting tips from the above post. The sensor is a two-wire device, a photo-diode or opto-switch, which leads to a BCM as is shown in my '00 WJ FSM.
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Old 10-01-2016, 01:57 PM
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Originally Posted by Cherryokee View Post
X2 what Willy55 said. It could be that as-well...

Upon reviewing schematics I believe I have misinformed you. Please disregard most or all of my theorizing and troubleshooting tips from the above post. The sensor is a two-wire device, a photo-diode or opto-switch, which leads to a BCM as is shown in my '00 WJ FSM.
yes I see the schematic as well. Hunting down the pins is the challenge, but, am thinking the sensor itself is a likely suspect.
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