Disabling automatic headlights/ambient light sensor

[Paul Bell]

This is to disable the automatic light system which is triggered by the ambient light sensor in the top of the dashboard.

The auto light system is NOT part of the daytime running light system (DRL). They are two separate systems, controls and functions. Performing this mod will disable the auto light system and leave the DRL system intact and working. If you want to disable the DRL, it’s a separate mod and procedure. This mod will NOT affect how the lights work manually.

The ambient light sensor in the dashboard is wired to the body control module (BCM) located in front of the rear fuse block under the rear left seat.

The mod is to simply find the two wires from the sensor, cut them and splice in a 1K resistor to the plug to the BCM.

It’s the bottom/smaller of the two plugs in the BCM.

Procedure:

Tools needed:

-1K resistor, 1/8, 1/4 or ½ watt;
-soldering iron & solder;
-electrical tape;
-wire cutter/stripper;
-flat screwdriver;
-18mm deep socket, 3/8 swivel, 10 inch extension & ratchet;

1: Remove the rear left seat using the 18mm socket. Set the seat aside.
2: Using the wire cutters, pull the pins holding the fuse block cover.
3: Using the screwdriver, pry the ring around the fuse block out to release four retainers;
<CAUTION> The large red power cable & stud has live 12 volt power!
4: Squeeze the retainers on both BCM plugs & pull out.
5: On the smaller plug from the bottom, locate the black & white wires corresponding to the pins below.
6: Clip both wires leaving about an inch and a half sticking out from the plug.
7: Solder the resistor to these two wires.
8: Tape the end of the wires from the harness.
9: Plug the plugs back in.
10: Reinstall ring, seat and cover.
11: Enjoy being in control of when your lights come on!

And this makes the seat bolt nuts way easier to remove:

 

[kickass audio]

Another idea too if someone wants to do it is to put the 1k resistor up in the dash into the sensors harness where it connects. It isn't that hard to remove that part of the dash at the top. Just grab it from within the vents for the defrost and pull up and back and then disconnect that plug for the light sensor and put the resistor across both wires (do not just shove it into the connector, it may work for testing but is not that good to do as it may fall out), One thing to note with that is it will only work on the light sensor where it has 2 wires. There is another sensor out there with more wires which iirc is for adjusting the hvac system.

 

[Paul Bell]

Yessir, you are correct about that, I saw it in the headlight schematics.

However, I would think that folks doing this would also want the DRL disable mod which is done at the BCM-as is the quad headlight mod.

In my particular case, I performed all three mods at the same time.

I am curious though, what does the automatic HVAC system need with an ambient light sensor? My truck has auto HVAC so I would've needed to do the auto-on headlight mod at the BCM anyway.

 

[The_Roadie]

The auto HVAC system uses TWO photodiode sensors in that dashboard dome, to tell which wide of the vehicle is sunnier. The sunny side gets more chilled air sent its way to satisfy the driver/passenger split controls. Since the system has temp sensors in the ductwork vents for each side, but the cabin airtemp only has one sensor near the driver's left shoulder. It's basically a passenger-satisfaction-enhancement-device.

 

[Paul Bell]

Very interesting information. These trucks are pretty smart, eh?

It looks like the auto ac system processes the signal from both sensors and sends one signal to the BCM.