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Discussion Starter · #1 ·
I am working on my Wagon and would like some lights on all the time while driving. Could someone post the serial bus diagram for the front [and rear would be great] fusebox. I have elctrical tech experience but am aging out on the thinking part I am afraid. I think Rodney posted some of this stuff not long ago. Thanks Gene

Here is some Sport Wagon porn for you. --- I really gotta replace the grille, but I am not sure I have another bumper on/off in me. Cardiac surgeon appt this week...
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'12 CTS Performance Sports Wagon AWD
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It is simple to do. I did this in my truck... Haven't done it in my car yet.. Thinking about having it setup to have the fog on with the brights... Since I am using LED fogs so they actually do something. (I use them mostly to see whats to the sides of me. AKA Deer..)

If you understand how relays work this is an easy job for you.
The relays have a power side (2 or 3 contacts depending if it supports both NC and NO positions or just one of them), and a switch side (2 contacts) The relays normally have a picture on the side of them that show which pins go to what. Should look similar to this...

Font Rectangle Parallel Slope Terrestrial plant

So what we care about are the 85 and 86 terminals. How GM does this is they apply power to one side of the coil and the other side goes to the controlling module which provides the ground.(in most cases the BCM).
It will connect the circuit when one side of the coil has power and the other has ground. The BCM can handle powering a couple of relays just fine. My truck I have the DRL on with the Headlights and I have all of the lights come on when the brights are on (Including the fogs).

Find some Small Diodes. You will pass VERY little current through them so the smaller the better. You will also want to have some wire to solder on each side. What I did was encase the wire and diode in heat shrink tubing where I could still see the Line on the Diode. (I just remember to put the line on the side of ground.) Since then i would have been better off running a red wire to the non-white line end and a black wire from that end. You want to then connect the diode between the Negative side of the coil on the relay you are going to trigger from to the Negative relay you are powering up. The part I forget is which side to put the white line on. You use the diode so you are not backfeeding through the relay and pulling on whatever relay you were powering from whenever the lights you want on are on. I want to say you want the white line aimed at the lights you want to power, that would prevent the backfeed. If I power a relay to run aftermarket lights I always just pull off the powered side of the relay to the power side of the coil on the new relay and ground out the other side on the new relay. This way I am still using very little energy but not adding any extra draw to the BCM. If I shorted out the wire at any time to the new relay with this method I would blow the fuse in the fuse box. if you were to power the new add on relay directly from the BCM it will work, but if you short it out you fry your BCM since it does not have any external fuses protecting its outputs. But within the fusebox, as long as you understand what you are doing, you won't blow anything.
 
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Discussion Starter · #4 ·
Thank you sir. I have done that several times, just wondered what sorted out the buss signals and provided a voltage or ground to the relay. And it that might be a better way to do it. Overthinking with an addled brain [I have severe sleep apnia and they cannot come up with a treatment that works, some days I have a brain and some... not so much]. Gene
 

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The relay coil sides are directly connected to the BCM, without fusing. Otherwise you can splice into the output of the relay after the fuse and trigger a relay that comes off the positive bus for its power. I did this in my Avalanche for a backup for the lights so I could pull the diodes back out.. There are some smaller relays that are available that do 10-15 amps and are pretty small. More than enough to run most lighting.

With those relays, I have the ground side of the relays coil going to a ground. I have the positive side of the coil pulling off the powered output of the relay its being triggered from. I then have the power going to the relays pulling off the Aux power post that is in the fuse panel. You could most certainly do the same sort of thing.
 

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Discussion Starter · #6 ·
thanks again- I imagined there was a module under the fuse box decoding the buss signals and energizing the relays. I restored C2 and C3 corvettes for 20 years and then got into a field that actually paid off well. So I am trying to catch up with modern car-cars. Gene
 
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