Relay Trigger to High Beam

[K5-Z71]

For the purpose of installing a lightbar which comes on with the high beams I've always used a trigger relay tapping into the high beam power where is most accessible - pretty easy task. However it appears GM simplified wiring on their end by having the Lighting Control Module send PWM voltage signals to the Headlamp assembly where it will internally switch on/off the various functions. There is no longer an easy 12v trigger externally available.



Does anyone have an idea how to get a trigger to activate a light bar?

If not it looks like ill be doing some experimenting with a Current Sensing Switch. The idea would be to route the GND side of the headlamp through the switch and adjust the current sensing to only activate when it sees the additional current that the high beams draw.

I would appreciate it if someone had a better idea than mine...

 

[WalleyeMikeIII]

Put an oscilloscope on the three PCM lines…trigger the various lighting positions…observe the signals, then calculate the average DC voltage and build a trigger on that voltage?

 

[jgraves]

No ideas of the top of my head but I'll likely be tackling the same issue. On my old truck, I tapped the high beam fuse to trigger the aux lights. I haven't looked to see if the same would be applicable with the LED headlights in the new trucks.

 

[K5-Z71]

I think I'm onto something here. Headlights with DRL draw 1.41 amps while the high beam draws 2.08 amps.turn signals consume same current as DRL.

I did get the current sensing switch in the mail and verified it's operation within these values.

My tuck hasn't gotten the software update that dimms the DRL when the high beams come on so that may require some adjusting.

A few more loops of the power wire passing through the switch will double it's indicated power draw so I'll do that on the final install to give it better resolution between high beam and low beam.

Who knows when I'll get time to rip off the bumper and fabricate brackets but when it's finished I'll post up!

 

[66 Galaxie]

Nice work. I’m looking forward to your next update.

 

[K5-Z71]

Here's the plan. The switch with an astric is the current sensing switch which can be adjusted to trigger at whatever amperage value is needed. I also purchased the Rigid Industries DRL light bars which have a high and low setting.

The tuck's side marker light activates the first relay to deliver power through the NC side of the second relay to power the AUX Light Low setting.

The current sensing switch monitors the Truck's headlight power draw to determine whether the high or low beams are active.

When the switch sees over ~ 2amp it triggers a relay to remove power from AUX Low and provides power to AUX High.

I'll also have to wire in a three way switch to provide a system shutoff, normal operation and manual activation of AUX high.