HOW TO: Wire up your LED/aux lights to work with CAN-BUS driven hi/low/parking headlights.

I appreciated your input on not interrupting the signal to the fog lights and I would have had to interrupt both.
I was able to do it with just a signal from one of the fog lights by incorporating the light bar relay into the plan. (see post above).

And yes, I would never use parking / taillights as a power source for the light bar. The original diagram that I posted literally said "To Light Bar Relay #86". I thought it was obvious that relay would have it's own proper power source. Suppose I should have specified that.

In the end, I tapped the positive wire to the fogs and the parking light feed at the tailight. No too invasive considering I was willing to tap the high beam signal if there was one. I think people are tapping into the taillight for the lighted rear fender flares so same same.

 

great post! thanks for the write up

 

Next level would be a switch on the dashboard to interrupt power to the lightbar. (I would use another relay)
This would allow normal headlight functions while having the lightbar off.
I could easily add the switch but I like the fact that I didn't have to go thru the firewall or under the dash to this point.

So yes, code officially cracked, light bar function with high beams ... without a $120 Canbus reader.
Really no downside to this method if you use a switch.

 

While the dual relay works, it does not replace the canm8 functionality. The canm8 functions independent of fog light status. In my case, the high on signal from canm8 routes to a dash enable switch then to relay to drive the light bar. When switch depressed, light bar can only come on with highbeam. Often, if I'm in a urban area, I'll have my fogs off to reduce reflections. The dual relay approach as described will have the lightbar on with low beam by default. This drives adding a on/off switch that you must remember operate when you turn the fogs off. With canM8, not need to remember turning high beam switch on/off.

For clarity, the cost is greater than the canm8 alone. Waterproof connectors (weatherpack or metri), fused terminal block and quality relays, lined shrink are not trivial $$.

 

That's the advantage to adding a switch (which usually comes with the light bar anyway). You can run headlights without fogs and without the light bar by cutting power to the light bar with the switch.
So no drawback function wise

As far as the cost, does the cambus reader eliminate the need for a waterproof relay with waterproof connectors? Fused terminal block? No other wiring, loom, ties, connectors needed?
I can list the components that I used that didn't come with the light bar and it literally would be about $20-$30. Although the components may not be up to your standards if you're spending $35 on a relay and adding a fused terminal block for whatever reason.

I won't go so far as to say the cambus reader is a waste of money. It definitely makes the job faster/ easier ... but there is another way if someone wanted an option.

 

With the canM8, don't need to remember to use a switch to kill the lightbar when fogs are off which is important to me as I'm not the only one driving the vehicle.

With the canM8, at least my install, the wiring is interior, waterproof would not be required. I did use a fuse block as I also run puddle lights and compressor. They are loomed and shrink wrapped. Lightbar came with a weatherproof pigtail.

CanM8 may not be faster install as carefully opening the dash for install is not trivial.

The relay solution is novel and will work for some, but it's not the same function a canM8 provides.

 

Relax kids.
We're slowly turning this into a pissing match, for no good reason.
( I can easily say "well, if your fog light circuit blows a fuse/etc your lightbar is rendered useless; if your truck never came with fog lights what would you do?...etc")

Both solutions achieve the same outcome; thank you for sharing your approach as a viable alternative to the CANM8 device/solution.
We could argue benefits of one vs another approach for some time, and ultimately it's up the user/installer to decide which "system" they want.

IMO the "double relay/fog lights" method is basic, in design/execution.
CANM8 is "advanced" as I see it.

Last, but not least example and something to consider:
Most (perhaps) ppl in this thread as interested in "light bar ON when high beams ON" solution, but as I exemplified before, the multiple output CANM8 device is awesome for anyone (me, for example) that wants to use other "triggers" from the truck's lighting system for additional functionality.
Instead of running multiple "double relay" solutions (or who knows what other ways to get a trigger), I love the fact that a single small box can simply read the truck commands and give me "high beams ON, low beams ON, parking lights ON, etc" outputs.
Through 1 easy solution I have long range light bar on with high beams, aux/amber fogs with low beams ON, and could have used other outputs for a myriad of applications.

To each their own I guess...
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