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2011 Kia Optima
38 Posts
Discussion Starter #1 (Edited)
Vehicle: 2011 Optima LX MT
Difficulty: Moderate
Time: ~3 hours

The Auto Light Sensor is located in the center of the dash and has 2 functions.

1. Turns the Headlights on when it gets dark.
2. Dims the interior illumination when it gets dark.

For cars without factory Auto Lights the sensor and wiring is missing. However, the BCM is programmed to handle the input if the sensor is available. I had all of the parts lying around so this was a free mod for me but there’s maybe $1 of parts here plus the $9 shipping you’d pay and this is a $10 mod. Here is the schematic for the sensor the way that I made it.

Required Tools:
Panel Remover
Soldering Iron
Hot glue or equivalent
Small screwdriver

Required Parts:
Photocell (I used 50ohm - 70kohm light - dark)
Variable Resistor (I used 5kohm, 25 turn)
Wire (24 awg will do)
Connector Pins (I got mine from an old ATX power supply)
Zip tie/Twist tie
Electrical tape
2-pin connector (Optional, I used a trailer connector)
Heat shrink (Optional)

Step 1 - Remove the factory alarm light cover with a panel remover.

Step 2 - Remove the Black Plastic Cover. (The Service Manual shows the whole module coming up several inches so that you can unplug the connector but this is as far as I could pull mine up.) There is one tab on each side and one on the back that need to be released.

Step 3 - Drill the cover so that the photocell will fit in.

Step 4 - Solder wires to the photocell. (30” should be long enough)

Step 5 - Install the photocell in the cover with hot glue or your favorite equivalent.

Step 6 (optional) - Solder some sort of connectors to the end of these wires and heat shrink as necessary.

Step 7 - Solder wires to a variable resistor. Take note of which way to turn the resistor to increase/decrease resistance. I also recorded how much the resistance changed per turn. One wire goes straight to the BCM, the other connects to the BCM and one of the wires coming from the sensor (via the connector). The other side of the connector goes to the BCM as well. Insulate/heat shrink/electrical tape as necessary. (I forgot to take a picture of this step so this is just a mockup, I’m always careful on these trailer connectors to put the better insulated end on the energized wire.

In the car:

Step 8 (optional, this can be done in the car) - Plug the connector together and test it. Put 5V on the wire going to the sensor and 0V on the wire going to the resistor, measure the voltage across the resistor. The headlights will turn on at anything less than 1.75V. A well lit room is close enough to a good trigger point so with the sensor in that environment adjust the resistor to get about 1.75V.

Step 9 (aka the fun part) - Run a wire/hanger/fish tape down the hole in the dash towards the accelerator pedal. Then pull the connector on the sensor (or the whole thing if you skipped step 6) all the way down. This took me probably 15 minutes or more as I didn’t have a proper fish tape and everything kept on binding up.

Step 10 - Connect the wires to the BCM Connector B (back bottom, aka M02-B).
5V (to sensor) - Pin 10 (Purple, Factory is Brown)
Signal (to resistor and sensor) - Pin 17 (Grey, Factory is Blue)
GND (to resistor) - Pin 16 (Green, Factory is White)
It’s much easier to add pins if you take off the small plastic strip on the sides.

Step 11 - Plug everything together and test. There is a 15s delay unless it is REALLY dark. Covering the sensor should turn the lights on. You may need to use a flashlight to get them to turn off again.

Step 12 - Snap the plastic cover back on the alarm light and snap the whole module back in the dash.

Step 13 - Zip tie/twist tie everything up above the BCM to keep everything away from the pedals while driving.

Step 14 - Adjust the resistor to your liking. Increase resistance to make the lights come on in darker conditions and decrease resistance to make the lights come on in brighter conditions.


Super Moderator
2012 Kia Optima
3,486 Posts
Very good write up. And probably works between than the cars that come with the darn photocell! ha
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