GMT800 DRL Ambient Sensor Questions - Lil’ Help Pls

Doubeleive said:

well a tech2 would be ideal I guess but you can get to the sensor from under the dash, I would confirm it is not working by covering it in daylight with a dark towel and see if the interior lighting goes dimmer or not. you might have to either use a flashlight and some long needle nose pliers or grab the sensor cap from above and try twisting it counter clockwise and it will come loose so you can remove it from below
sometimes the harness comes off the bottom and that could be a reason why it is not working, you should be able to see if it is attached with a flashlight.
if you can't get to it from below then you may have to cut the metal bracket that is behind the radio to have access, but I would try moving any wires or foam padding out of the way and try reaching in there it's tight but can be done with fingertips.
not sure if would be 2 wire or 4 wire you should be able to see it again with a flashlight

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JCODOHERTY said:

I will be checking the sensor's connector in the morning. I replaced the sensor and DRLs aren't switching on. The head lamps are on instead. Swapped relays and no change. If it isn't the relay or the sensor or the new sockets and new 4114LL bulbs it has to be the big diode under the dash?

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Doubeleive said:

have you tested the drl fuse?
there is no "big diode" that I know of anyway, there is a "sun sensor" which works as the daylight sensor and also works as a sensor for the hvac. make sure it is connected to the harness and twisted into its slot in the dash properly
sometimes they get worked loose and fall inside a bit or the harness can be disconnected.
the space under the dash (behind the radio) is pretty tight you need a flashlight to see in there, probably a little bit of foam in the way that can just be pushed down or taken out.

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