MrScottly
Well-known member
2025 HD ZR2 Duramax... In the past people would use fuse taps to trigger the light bar from the high beam circuit in the fuse box. The new LED lighting doesn't allow you to do that, as each headlight is it's own module and those modules are controlled by the LCM (lighting control module), located under the dash next to the BCM (body control module). It is the smaller of the two modules.
To solve this problem, I ordered a trigger circuit from Amazon
This circuit requires 12v power and only 3mA to trigger it. It engages a relay which can switch on or off. The trigger voltage can be Positive or ground...Interchangable by plugging the jumper into the proper holes on the board. I used positive.
I mounted the board in a small box
I used a three wire connector on one end of the box and a two wire connector on the other.
The board has a 10amp relay, not enough to power most light bars reliably. But, the relay on the circuit board is used to power a 30amp relay that runs the light bar. If using a wiring harness supplied by the manufacturer, you are effectively replacing the switch with the circuit board relay.
The high beam circuit in the truck is activated by the turn signal lever, which sends a momentary ground signal to the BCM, which in turn sends a signal to the LCM, which then sends PWM (Pulse width modulated) voltage to the headlight module. This PWM is constant, and is the signal you will use to trigger the circuit board.
This signal is located in the white wire, coming from the green plug (pin 11) from the LCM. (see pics)
Run a wire into the cab and tap into this wire...it is the signal wire for the circuit board.
While the light bar relay gets power straight from the battery, the circuit board should get power from a keyed power source...I chose Fuse #40 in the fuse box located on the driver side, next to the battery. I used a fuse tap to pull the power from it. The circuit board uses a very small amount of power, and using this fuse has not triggered any CELs.
See pics below. Any questions, ask.
To solve this problem, I ordered a trigger circuit from Amazon
This circuit requires 12v power and only 3mA to trigger it. It engages a relay which can switch on or off. The trigger voltage can be Positive or ground...Interchangable by plugging the jumper into the proper holes on the board. I used positive.
I mounted the board in a small box
I used a three wire connector on one end of the box and a two wire connector on the other.
The board has a 10amp relay, not enough to power most light bars reliably. But, the relay on the circuit board is used to power a 30amp relay that runs the light bar. If using a wiring harness supplied by the manufacturer, you are effectively replacing the switch with the circuit board relay.
The high beam circuit in the truck is activated by the turn signal lever, which sends a momentary ground signal to the BCM, which in turn sends a signal to the LCM, which then sends PWM (Pulse width modulated) voltage to the headlight module. This PWM is constant, and is the signal you will use to trigger the circuit board.
This signal is located in the white wire, coming from the green plug (pin 11) from the LCM. (see pics)
Run a wire into the cab and tap into this wire...it is the signal wire for the circuit board.
While the light bar relay gets power straight from the battery, the circuit board should get power from a keyed power source...I chose Fuse #40 in the fuse box located on the driver side, next to the battery. I used a fuse tap to pull the power from it. The circuit board uses a very small amount of power, and using this fuse has not triggered any CELs.
See pics below. Any questions, ask.
