gary
08-29-2005, 10:27 PM
Background Information
I have seen several articles on how to disable auto headlights on earlier BCM controlled trucks. None of these articles seemed to cover my 2003 as I had more connectors on my BCM and they were different colors.
Theses articles described the sensor as being a photoresistor and recommended bypassing it with a 1kΩ resistor.
I visited my dealer today and they were kind enough to print a schematic of the circuit. It turns out that on the 2003 the sensor is a photodiode. The anode of the photodiode is connected to the BCM through a white wire terminating on connector 3, position A4. The cathode is connected to the BCM via a black wire terminating on connector 4, position B7.
A photodiode conducts when exposed to light. Since the sensor is a photodiode, I chose to bypass it with a diode. This way the BCM will still see the characteristic 0.7 volt drop. It may work fine to just bypass with a wire, but I didn’t test this.
Connector 3 (C3) is 24 positions and brown, and connector 4 (C4) is 24 positions and light blue. Looking at the BCM from its rear side (side facing the drivers seat) C3 is the center connector and C4 is to the right.
C3 and C4 are both two rows of 12 pins, with ‘A’ row on the bottom and ‘B’ row on the top. Position numbering starts on the left as the BCM is mounted in the truck, looking at the backs of the connectors.
Procedure
Obtain a garden variety silicon diode. I used a 1N4003 (RS 276-1102).
Solder solid wire leads, about 6” long, to the diode and insulate the connections. I used 20 gauge wire and small heat-shrink tubing. Don’t cover the stripe on the diode as this marks the cathode and you’ll need to know which end is which.
Strip about 3/8” of insulation off of each wire and fold the stripped wire back over itself to create a pin connector.
Remove the lower driver’s side dash panel.
Locate the BCM, which is centered below the steering column.
Locate C3 (Brown) and C4 (Light Blue).
Locate position A4 on C3. This should have a white wire coming from it.
Insert the anode end (no stripe) wire into the back of C3 at A4, along side the connector pin. Friction should hold the wire in place. Adjust fold in wire as necessary to achieve desired friction connection.
Locate position B7 on C4. This should have a black wire coming from it.
Insert the cathode end (stripe) wire into the back of C4 at B7, along side the connector pin. Friction should hold the wire in place. Adjust fold in wire as necessary to achieve desired friction connection.
Using small nylon wire ties, secure the wires so that they will not vibrate loose. Fold the diode into a safe position and secure.
Cover the ambient light sensor on the top of the dash, to simulate darkness, and turn the key to ‘on’. Your headlights should not come on.
Turn the key off and replace the lower dash panel.I have no idea what might happen if the connections were made incorrectly. It might damage the BCM, or it might not. Perform this modification at your own risk.
I have seen several articles on how to disable auto headlights on earlier BCM controlled trucks. None of these articles seemed to cover my 2003 as I had more connectors on my BCM and they were different colors.
Theses articles described the sensor as being a photoresistor and recommended bypassing it with a 1kΩ resistor.
I visited my dealer today and they were kind enough to print a schematic of the circuit. It turns out that on the 2003 the sensor is a photodiode. The anode of the photodiode is connected to the BCM through a white wire terminating on connector 3, position A4. The cathode is connected to the BCM via a black wire terminating on connector 4, position B7.
A photodiode conducts when exposed to light. Since the sensor is a photodiode, I chose to bypass it with a diode. This way the BCM will still see the characteristic 0.7 volt drop. It may work fine to just bypass with a wire, but I didn’t test this.
Connector 3 (C3) is 24 positions and brown, and connector 4 (C4) is 24 positions and light blue. Looking at the BCM from its rear side (side facing the drivers seat) C3 is the center connector and C4 is to the right.
C3 and C4 are both two rows of 12 pins, with ‘A’ row on the bottom and ‘B’ row on the top. Position numbering starts on the left as the BCM is mounted in the truck, looking at the backs of the connectors.
Procedure
Obtain a garden variety silicon diode. I used a 1N4003 (RS 276-1102).
Solder solid wire leads, about 6” long, to the diode and insulate the connections. I used 20 gauge wire and small heat-shrink tubing. Don’t cover the stripe on the diode as this marks the cathode and you’ll need to know which end is which.
Strip about 3/8” of insulation off of each wire and fold the stripped wire back over itself to create a pin connector.
Remove the lower driver’s side dash panel.
Locate the BCM, which is centered below the steering column.
Locate C3 (Brown) and C4 (Light Blue).
Locate position A4 on C3. This should have a white wire coming from it.
Insert the anode end (no stripe) wire into the back of C3 at A4, along side the connector pin. Friction should hold the wire in place. Adjust fold in wire as necessary to achieve desired friction connection.
Locate position B7 on C4. This should have a black wire coming from it.
Insert the cathode end (stripe) wire into the back of C4 at B7, along side the connector pin. Friction should hold the wire in place. Adjust fold in wire as necessary to achieve desired friction connection.
Using small nylon wire ties, secure the wires so that they will not vibrate loose. Fold the diode into a safe position and secure.
Cover the ambient light sensor on the top of the dash, to simulate darkness, and turn the key to ‘on’. Your headlights should not come on.
Turn the key off and replace the lower dash panel.I have no idea what might happen if the connections were made incorrectly. It might damage the BCM, or it might not. Perform this modification at your own risk.